1) Dice
2) Little pad of paper+pencil
3) Minis and somewhere to put them
4) Vodka and/or coffee, as appropriate to time of day, company and genre
5) Background music (when appropriate)
6) Poker chips for money and other props (haven't tried this yet, but will do at the very next campaign)
Laptop (as a DM or as a player)
Projector or another monitor
Printer (for counters, maps, handouts, etc.)
Wireless access
chips for hit points
handouts for expendable resources (potions, wands, etc.) and status condition effects