I would hope that this would go without saying, but if you've got a Nintendo 3DS, bring it to TFcon and let's play some games!
I know some people are interested in bringing their 3DS for Animal Crossing and doing Spotpass. I'm hoping to get some multiplayer action happening because a large gathering like this is too good of an opportunity to pass up.
Here are the games I own which have Local multiplayer. Some of them have Download play too, so not everyone needs to have their own copy of the game in a few cases.
Mario Kart 7
New Super Mario Bros. 2
Mario Tennis Open
Super Street Fighter IV
Code of Princess
I have a bunch of other games that are single player only, plus a large stack of regular DS games.
So, post here if you've bringing a DS/3DS and what games you're bringing or want other people to bring.
I'll try and remember to bring my 3DS. But I don't really have any multiplayer games for it. I'll probably bring Pokemon Black 2 though. So if anyone wants to trade some Pokemon, LMK.