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.
Place this bait in an airtight container so it does not dry out.
Mould a pinch of 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.
Another good bait is very small strips of bait hung right off the bend of the hook.
For a wider look at using bait, see Better Bait Basics.