To sweep up large areas, like fields and fairgrounds, use a tow-behind powered lawn sweeper. These beasts will pick up practically everything up to an inch in diameter.
Gravel, stones, bottle caps, and even little stuff like lawn clippings and pine needles are no match for a gas-powered tow-behind lawn sweeper. They hold a fair amount of debris, so you can clean larger areas more efficiently.
Hook this up to the back of a lawn tractor, and you can sit down while you ride your way to a clean field. If you have a large enough crew, you can have a couple guys working backpack or walk-behind leaf blowers to push the debris into rows for the sweeper to pick up more quickly.
Nooks, Crannies, & Grandstands
While walk behind leaf blowers can move large quantities of trash and leaves over massive open areas, they aren't ideal in tight spaces.
A stadium job, for example, should begin with blowing trash out from under grandstand seating, blowing it down the stairs, moving trash from entrances and under bleachers.
For these kinds of spaces, it's much easier to use a backpack blower. Once you're finished blowing the mess out of the nooks, crannies, and grandstands, you can move it all into a pile with a walk-behind blower and haul it away to the city dump.