Baking bread for fishing bait
What about seitan (wheat gluten) (also available in dried form as e.g. chips) 



or fried (and dried, not shown in the picture) tofu bits



or tofu skin?



Pro: All these kinds of food are dryable and rubbery. 
Con: I suspect that you can't make this at home - it would be very time-consuming. (Hm, except the tofu. Buy fresh tofu, slice them into little cubes and fry them. Anthoer con: this might by much more expensive than baking bread :-)