Onions are a favorite of mine - for white or sweet onions, cut rounds across the grain (like making rings) then skewer them with bamboo skewers (I go through a TON of bamboo skewers, use em for everything), cover in olive oil, kosher salt, and thrown on the grill. Or if you're daring, just thrown em on without the skewers - you'll lose a few to the grill, but it's way quicker.
Green onions grill up nice after soaking in lime juice for 10-15 minutes - taste great on grilled tacos. Really really great. There was a time when I didn't fire up my grill without throwing a bunch of green onions on it...
One last grilled onion recipe - take a sweet (vidalia or walla walla type), and cut the sprout end off and pull the outer skin off. cut radially (like a pie) from the sprout end to the root leaving 1/2" at the root to hold things together. Wrap that up root end down in some foil, and top with butter, kosher salt, and a dash of balsamic vinegar. Sit those in indirect heat for 30-60 minutes (or longer if you're slow cooking at <200) and they'll get golden brown and delicious. Best grilled onions to ever top a burger or steak.
Last item of the night - I'm getting hungry - spuds. In addition to the old standby of grill-baking russets/idahos, I've got a few favs I pull out at most grill meals.
Red or purple potates - cut in 3/4-1" chunks and toss with olive oil, garlic, salt, and rosemary. make a foil tray, and fill half of it with the spuds, fold the other half over and seal it up to make a foil pouch. Throw that on the grill over moderate to high heat for 20-30 minutes, turning a few times (turn more often the hotter the grill is). Oh yeah, make sure you spray teh foil down with PAM - you don't want the spuds to stick.
You can do the above in a huge pouch (18x8 or so), or split it up into serving sized pouches to make more efficient use of grill space (they fit in between other things).
