i use cedar for my mice. just make sure there're no little bits on the animal before it is fed to the snake. as for substrate for reptiles (as that has been mentioned in previous replies),
i use pine for both of my pythons, aspen for both of my venomous, coconut bark for my red-sided skink, combination carpet and repti-bark for my nile, lizard litter for the blue tongue, and walnut shell for the agama.
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currently have:
blue tongue skink (skinky),
pygmy rattlesnake (gordon),
nile monitor (dick),
reticulated python (mousetrap),
egyptian painted agama (george),
ball python (snake'n'bake),
red-sided skink (skinky jr.)
mozambique spitting cobra (fluffy).