A simple tip for those times when you have things to give away randomly to your audience and forgot your bag of dice...
This site features a Random Sequence Generator which is simple, but effective.
Just have your audience count off, enter the count, then call out the first X numbers based on how many giveaways you have. Because it's a full sequence, you won't get duplicates and you'll have extra numbers if someone leaves or doesn't want a prize.
P.S. Here's an earlier post with five other presentation tips.