I use leftover aluminium pie trays for making craters.
I turn them over and cave in the 'base' of them, then glue them to an old cd (AOL cds are perfect - I still have a stack of them). Paint them brown/sand or black/grey and flock/add gravel and they work well.
Larger (family sized) pie trays work well for larger craters. I used to do the foam wedge with polyfiller, but these are easier.
Hey! Where'd ... Everybody ... go?