We have a remote control blimp at work which we fly around the lab when we're bored and/or slacking. It was filled with helium, but started to sag a bit. Since we didn't have a dewar of helium handy, we topped it off with hydrogen...

Then we named the blimp Hindenberg Jr.

(Fortunately, it contains only a liter or two of hydrogen and it's mixed with helium. Don't try this one at home, kids.)