Tip: Alien Blood Makeup for $1
Now here's something I really want to find an excuse to use. It's the same chemicals used in glow sticks, only in a more controllable package--the Glow Glove! I found this oddity in Dollar Tree (while shopping for fake human blood) and quickly took it home to be dissected. It's a clear, dopey looking plastic glove-within-a-glove with the aforementioned glow stick juices. Pop the inner packets and they mix together to give you a luminescent hand!
A better use for this is alien blood, of course. When Arnold Schwarzenegger injures the extraterrestrial Predator (1987), it bleeds glow stick. When I cut it apart, the glow glove had the chemicals needed in nice separate packets that you can combine later. The result is the same as cutting open a glow stick, only here you have way more control over the mess.
Of course, you don't have to use this as alien blood. It could be contents of a test tube in a mad scientist's lab or the big reveal of a victim's blood under a black light. You can do all kinds of stuff and let's face it, glowing practical effects are freakin' cool!