I need to be able to mix two liquids, and have them bubble, steam, or in some way cause a visible reaction, and still be able to drink it. Any ideas??

Colored water, a different colored water, and a couple alka seltzer hidden in the glass.

or if you're a tough guy, vinigar, colored water with baking soda disolved within?
I'm not sure that would work.

A small piece of dry ice in the water will cause a reaction. Just be careful not to drink the dry ice as that will ruin your day!