Lots of outdoor swap-meets where the weather permits. but it depends on what you're swapping. Lots of car-parts swap meets around here, and those are usually outdoors since it's often large, dirty stuff.

Flea markets are usually a mixed bag of used and new stuff and often have a permanent or semi-permanent location and set of vendors. Yard sales, garage sales, rummage sales, tag sales, etc. are usually one person/family selling their unneeded stuff out on the driveway.

Tailgating is partying out of the back of your truck. (Or it's when the jerk in the car behind you is following you too closely, but that doesn't apply in this context.)