The type that float away from the tube are the best and can be made from the collapsible metal fish baskets or mesh cloth laundry baskets. You need to to tie wrap a foam "noodle", like the ones sold as swimming pool toys, around the opening.

Caution: I do not recommend a mesh bag type that attaches to the side of your tube or pontoon because bluegill (and a lot of other fish) have spines. Spines and float tube don't get along! Trust me, I learned the hard way.