t-slots Yes
vacuum Yes
bubblegum No
Vise (get a good one), clamps, screws, double sided tape, contact cement, fixtures, and everything in between except holding it with your fingers, I ask my friends to do that
My stuff is straight forward enough that holding presents little problem, but it is getting more complicated as the parts get more complicated. I have seen fixtures what appear to be more complex then the part being machined.