Glowtini, definitely. And if that's the first drink you get, then the list is "every other drink you get, once you plop your glowcube into it"....glow-beer! glow-wine! glow-Beverly!
Just about any place that sells a mixed drink is going to have a drink that comes with a glow cube. It's a souvenir glow cube, which means you've paid extra for it, and it's yours to take.
Or you can find some online to buy, and just bring them!
I've also had the Magical Star drink...very tasty and has a glow cube.
I bought a package from a home/kitchen shop in Hollywood studios...I think they cost $6.50 for a two pack. This was in 2010...Sorry I can't recall the store name. I imagine you would be able to find them in other kitchen shops. They lasted us an entire year.
During each vacation, we've gone to the Sci Fi Dine In and they've always give the kids glow cubes. We also got them at the TRex restaurant in Downtown Disney.
we've never been given glow cubes as pposted above but we have purchased cubes for the kids drinks at places that have offered them for adults drinks and they just charge a few dollars for them to be added to the drink of yor choice.