I'm going through my BoB and other kits and have some stuff that have tops, lids, and various other things that I'd like to dummy cord to prevent them being lost.  I know a few knots, but I'm not an Eagle Scout or any sort of knot expert.  In my experience 550 comes untied pretty easily.  Is there a knot I should be using that's better than a simple square or overhand?

For example, attaching a length of hi-viz orange Titan Paracord


to an Exotac Firesleeve.

Double fisherman knot


http://www.animatedknots.com/doublefishermans/index.php?Categ=typebends&LogoImage=LogoGrog.png&Website=www.animatedknots.com#ScrollPoint

Bowline with an extra half hitch.

Cobra knot?

Are many uses for this knot,,+1

This is a good one.

There are lots of different ways knots are applied to the op's purpose. Sometimes the object just has a hole through which the rope is passed and then you just need a stopper. The fig 8 works well for that.

The bowline with half hitch has the working end hanging off at 90 degrees. Not a huge deal. But if you want a more finished looking job, the bowling with a double fisherman is nicer.

For really nice looks, the traditional climbing rig is nice. A fig 8 retrace with the double fisherman stopper.

I find that melting the finished knot with a lighter helps to keep it secured.  Not turning it into a blob, but just fusing the bends together,

Bowline

I run the cord through the item's attachment point and then put the two ends of the cord together and tie them in a figure eight knot.

Perhaps a lanyard (aka diamond) knot?

I use a uni loop knot to dummy cord stuff, but only because it looks cool.
http://www.animatedknots.com/duncan/#ScrollPoint

Take out the core, the knots hold much better that way, and it's not needed for dummy cords.  And melt the end into a blob and smash it down into the knot.

+1 for the double fisherman.  It's super easy, low profile, can be used as a stopper knot, safety knot, or looped back on the line to make an adjustable loop.  Plus, if you are trying to keep the line useful it isn't too difficult to get undone (usually).

This animation is for a double fisherman bend.  Anytime you see something called a "bend" it just means that you are attaching to ends of line.  If you want to use the double fisherman knot, just follow the instructions to make your paracord follow the path of the blue line and pretend the red line isn't even there.

I quit using 550 cord, which binds and dries out, when I found 2mm and 3mm round cord at Sportsman's Warehouse.  It's better in every way.  

I like the Bowline w/ Yosemite finish for its aesthetic appeal, but the figure 8 is quicker to tie.

I have 550 cord on my old LBE that was "Ranger rigged" back in 1984 and it's still holding up just fine.  

bowline is the knot you seek OP, that or the Lanyard knot noted above.  Also called a celtic knot.

I thought one of the ideas was to have as much 550 cord in your bag as possible just in case so fancy knots that had a bunch line in them was the goal.
With that said I have never gotten around to doing it myself.

Personally,  I prefer to have paracord and bank line coiled up and ready to use.  Every time I have undone some wrap or knot, the memory in the line makes it more difficult to use AND then I don't have the wrap/grab/handle/etc. that I was using the line for.

This is what I was taught"

 
My favorite knot.

As stated many times before, the Bowline is a great knot.  Easy to tie, easier to untie, it dies not lock up on itself.

And worthless as a knot to depend on in this application unless you add a stopper knot. When a bowline is not under tension it comes undone easily. I know you may have meant that but someone may read it unknowingly.

Side note on the bowline: teach yourself to do a "one-handed bowline". If you're ever hanging from a rope or need to quickly(catching a passing line from a boat and you're swimming, side of a cliff, whatever) attach yourself to one, it may save your life.
http://www.itstactical.com/skillcom/knots/save-your-life-with-a-one-handed-bowline/

Never heard of that one before, I'm going to have to practice with it but it looks great. Animated knots is a great site for this btw.

I "discovered" this knot a few years ago...  it is easy to tie and has a wide variety of uses...



YouTube Tutorial

The diamond knot looks cool.

I am a big fan of the double fisherman.. or in the case of this photo below, a triple(one more wrap).  It looks good as well, and is strong.

I did this, a loop of 7mm static cord tied with a triple fishermans, then put it into a klemheist(type of one way friction hitch) around the pole.  the harder you pull in the tails direction the tighter it gets and it wont slip on the pole.  This is my sail shade tensioner in my backyard.

Bowline is a horrible knot for that purpose as well.  Figure 8 FTW.

You can do a figure eight one-handed, wrapping it around yourself and securing yourself to the rope while being pulled along in the water? If so I am impressed. That's the type of thing I was referring to. Self-rescue, essentially.

The OP is asking about stopper knots on dummy cord items, using paracord.  Why are you giving examples of sinking vessels, dangling off cliffs, and one handed life saving knots?  Who is throwing out paracord to falling climbers?

I said side note, did you knot catch that?

Maybe you were agreeing to the first part of my post, not the second? I guess I don't care, no need to hijack the thread. Figure eight or the lanyard knot look great for the OP's purpose.

I think, in general, a small handful of knots will get you through most situations where cordage is a suitable material. The trick is knowing when to use each knot, and why you're NOT using a different one.

I really like the Figure 8 Follow-through/On a Bight, instead of the bowline, when using 550 or small cord/rope. They often serve the same purpose in this context, which is either to go around something being lifted or around something upon which you're pulling. The Figure 8 is really easy to tie (and fairly easy to untie) with 550 cord. It's easy to adjust, and it does not require a finish knot to keep from untying. The bowline usually requires a finish knot or a Yosemite finish.

The Figure 8 also plays right into the inline figure 8, which is one of the other knots I think you should know for 550 cord. The inline figure 8 is a directional knot that can be tied in the middle of the line and used as part of the modified trucker's hitch, which you need for putting up tarp shelters, and general line tensioning.

The double overhand is a good finish knot to know, but I use two half hitches more often, because I can untie them a lot easier. For permanent loops, double overhands made into a bend make a Prussik loop. It works fine for your dummy cord use, too. A prussik loop can be used for a bunch of tension holding or anchoring options on a line, outsde of the normal climbing and rescue uses.


Generally, this entire thread should help most folks recognize that if they don't know what the above knots are, and how to use them correctly, they may want to learn more.