you did what you could, Heather
very likely that little snake had other stuff going on too
not sure what to tell you about the crickets
do you know someone with an animal that will eat them?
you could always bring them back to petco and tell them that garters don't eat crickets - it's the kind of something they should know
in fact - tell them to look at the petco care sheet for garters
meanwhile
welcome to the forum