I've got a rough budget of $100 for 10 days/9 nights (just me and a toddler). I think that will work out to..
$18 for mousekeeping
$10 for one boozy drink (I'll probably actually split 2 of them with my sister, since we're both lightweights)
$45 for souveniers (most likely a pair of mouse ears for the toddler if she'll tolerate them, and a CD for me)
$27 for misc (possibly more souveniers, extra tips, snacky things, etc. This is the trip slush fund.)
It's all pretty flexible though, if we want more snacks, we'll get less souveniers, if we want more stuff, we'll have less snacks. If we have a major problem (I'm recalling rotavirus here), then I'll blow the budget, but I don't anticipate that.
DME for transit to/from the airport, bringing our own stroller, no refillable mugs, etc.
Edit: Oh, I forgot, the other souvenier thing is pressed pennies. I'm bringing about $8 in change for that, and extra cleaned pennies. If she likes it then we'll get a book and I'll get more quarters. So I suppose the real budget is $108.