That's a nice little shopping spree. You might want to consider returning that sander for a mouse sander, the pointed tip comes in handy for getting into odd corners and such. I use it a lot more than my round and square palm sanders.
Also, look for a very small, fine file set, something like this:
Busy Bee Tools Item Detail
Dirt cheap and I use them more than the bigger ones.
You have a dremel already? Handiest tool of all....What size hole saws are those? I think I see 4" BTW, that's a kick arse drill
If you're looking to spend more then you can always get a jig saw but really the dremel is the key, that tool can do almost anything with the right bits.