OK, here's our "Isle of Man" sidecar / pitbike (great for carrying tires, fuel tanks and one passenger). We just got back from the PVGP and it got more notice than my race-Sprite.
Saw this one last week at PVGP. It's at a lot of vintage events I run. Usually, the "deck" has tires, people, or fuel cans (for the owner's Cobra) on it.
To be honest, I think this is the simplest and most effective pit cart. Cheap too.
Saw this at BeaveRun last year:
Seen at Lime Rock a few years ago:
And this is Chris Shoemaker's Moke that he always brings to VRG vintage events. We were in at the PVGP last week. It's street legal and great for running out to the local store when away at a race. He has enough extra room in his car carrier for it. It's sort of a communal "pit cart". We used it for our Xmas card picture a few years ago.