I work hard on trying not to make my goodbags junk. We have done a few things, but ours usually match a theme. If you want to go with your art idea, which I think is great, go to Michaels. They sell small kits for $1, It comes with a wooden animal to paint, three small paint tubs and a paint brush. We got these at a party once and my kids loved them. We saved them for a rainy day and it was great.
As for prizes, I don't really do prizes at our parties. We tried that for my son's 4th birthday (that's when we do our first "big" party) and the kids who didn't win were upset (even though I had something for everyone). Kids wanted to change prizes. Some kids just wanted to watch and didn't want the prizes. It just didn't work. So from then on the games were just for fun, no competition. Everyone has always seemed ok with that.
AS for the pinate. I have to confess...I have filled ours with candy from Halloween in an attempt to get it out of our house. It's hard to come up with things to add to it that don't fall under the "junk to toss later category". Some things I have added or seen added that were not candy...small bottles of bubbles (you do have to worry if they pop open, everything gets soaked in soap), glow sticks and bracelets, small packages of crayons, stickers, tatoos, matchbox cars. I think my favorite was the pinate that had stick on mustaches included. It was just fun to see most of the kids sporting a 'stache. :)
Have fun.