The bait I use most often needs to be prepared before the trip.
Slowly add cooking oil to about a full cup of flour and mix, till it forms a thick paste about the consistency of plasticine, or Play-Doh. Even better is to use fish oil, or the oil from a can of tuna or sardines.
Mould the bait around the bend of the hook, trout hooks are best, so it forms a shape and size much like a grain of cooked rice.
For a wider look at using bait, see
Better Bait Basics.