added part about printing certificates to hand out codes
Timing is critical. Giveaways immediately after lunch go faster because most attendees come back to the room for the next session. Slots after a poster session or between lightning talks and breakout sessions are much slower, as many people choose to take a break and not return to the room. It is therefore necessary to call lots of names before selecting someone present in the room. Giveaways on the final day are avoided since attendance is lower that day.
For fun, have a sound tech add a drum roll.