First off, ditch the crickets. Not in their diet. No bugs.
You are better off staying with worms(night crawlers/earthworms), pinky mice and safe fish(Guppies, Mollies), high quality store bought fish(Salmon, Trout, Tilapia)

They will eat toads and frogs but they usually carry a heavy parasite load.

Garter Snake Care Sheet - Caresheets