Peanut butter and whole peanuts in the shell are the best choices for bait to use in a squirrel trap. Spread the peanut butter on the pan, and then stick the peanuts still in the shell into the peanut butter.
Put the bait before and after the trigger, as well as leaving a small trail leading into the trap. This is the most effective presentation. In some cases where the squirrel is inside an attic or the interior of the home and is stubborn, oranges are a good option. The squirrel can detect the moisture in the orange and if it is thirsty, it comes out to eat the orange pieces.