I would recommend Canadian Nightcrawlers. They are large, very nutritious, make a great staple, and are fairly inexpensive depending on where you buy them. They also live for a long time if kept in the fridge. Some Walmarts sell them for about $3-4 for 20 (I think), Petsmart sells packs of 12 for $4-5, and a lot of bait shops sell them at varying numbers for varying prices, but usually not too expensive. You may need to be careful about some bait worms, depending on what they were grown on and if they have any sort of dye in them (for the purposes of attracting more fish). I have never seen this anywhere, but have seen other people caution about it. Good luck!