I use Smooth-On because they have been reliable.  They are also here in Easton, PA which means I can drive to them and pick it up (saves on shipping costs/time). ÂÂ
The scale you can pick up at Wal-mart for $10 although it isn't reliable for small weights.  Luckily Smooth-On allows you to mix by weight or volume.  As for cups and such, I just go to Party City and pick up clear plastic cups that you would use at a party.  They are sturdy and you don't feel bad about tossing them. I also wash out and use juice caps and fruit tubs (those little plastic apple sauce or fruit cocktail containers that are kid sized) when I want to mix small amounts.  This was necessary when I did the Dark Eldar models since the resin amount was so tiny- even with three molds I wouldn't even use a cap full of resin.
Popsicle sticks for mixing sticks.
Don't mix near your models. ÂÂ

 Or in clothes you like. ÂÂ

Oh, as for Legos they are great for building mold boxes but expensive. Megablocks or the knock-off Legos work just as well and are half the cost. Pick them up at Toys R Us.
And O-man is right - eye protection is a must. The mold release stuff is great for keeping your molds from deteriorating but it will melt your eyeball.

Well, maybe not MELT it, but it will do something very, very, very bad.
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author of Syncing Forward and other stories...It's a dog-eat-dog world, and I've got my Milkbone underwear on.