In the last few months, I was doing some trail clearing in the back woods of my yard, and carrying the various tools was getting to be a pain. I have a 4 wheeled garden wagon, but that is pretty large, and actually unwieldy, and would really not pull very easily up the hill and around the fallen logs and debris in the woods. So in my head, I was considering throwing together a simple 2 wheeled cart, with a wood flatbed sized to hold 2 milk crates. The crates would hold my tools, and on top I could strap the shovel, rake, etc. I'd use small 20" bicycle tires or something similar.
In my daydreaming mind, I also imagined this could make a good range cart for bringing my rifles and ammo along when I shoot at a particular spot a half mile down a trail in the back woods.
An image search on google has tons of ideas, and one item I came across seemed particularly well thought out.
A small aluminum and stainless steel bicycle cart made in Germany. It is set up to be towed behind a bike. The tow arm can be removed and rotated to pull or push it along by hand. And it even has a pull out handle (like what you see on wheeled luggage) so that the cart can be used upright, like a hand truck.
Overall a pretty ingenious device. Not cheap at over 400 Euros, but looks very well made, and fabricated in western Europe. the hmax by hinterher.
http://www.munich-biketrailers.com/shop.php
A sled... They actually have a kit that you can convert this into a sled...
Personally, the trailer bed is just a bit too small for my uses, I would try to put one together that is a about 25% larger, but overall a clever set up.