So I've got two 3 lb chuck roasts that I'll be slow cooking.  First one will be with cream of mushroom, lipton dry onion and water with some potatoes and carrots.  

gonna cook on low for about 8 hours.

What should I do with the second one?

I do a lot of pepper and lightly flour, brown in oil in a cast iron, then move it to the crock pot on top of a halved onion broken in to pieces.  I don't like to make my onion small.

Then I dump my mushrooms in the cast iron and brown them in the extra oil.  Add flour to thicken, and tomato paste for flavor.  Once it's ready, I pour in a carton of chicken stock, add rosemary and thyme, bring to a simmer, and pour the whole thing over the roast.

I put as many carrots as I can fit over the top.  Low for 6 or 7 hours.  8 hours has always been too much for me.

Google "Mississippi Chuck Roast". An amazing, easy and different way to prepare a roast.

make a faux barbacoa for tacos

I cook mine dry.
Rub some Kitchen Bouquet on the roast, dust with flour and seasonings.
Put in the crock pot with no liquid or veggies.
I sometimes slice an onion or put some pepper rings on top of the roast.
Cook on low for 8 hours or so.
When it's done there will be plenty of liquid from the roast to make gravy.

This for an easy, good meal.

I only add a pat or two of butter, not the half or whole stick some recipes suggest.

This coffee and soy sauce roast recipe is fantastic.
basically turns into an 'au jus' flavor.  you'd never know there was a cup of coffee in the recipe
I've done variations of it with a small chopped onion and a bay leaf.  Either way I think this is a great start to a roast.

My wife isn't a big roast fan so I normally just salt heavily and let it rest in the fridge for a day, add pepper & garlic, then fully cook until fork tender. I pull the roast out, shred it, throw home-made egg-noodles in then add shredded roast back on top. Best beef-n-noodles ever!!