Consider a raffle
Few things can bring people out to a company picnic easier than a raffle where some lucky employee will walk away with a new stereo system, television, or guitar. Competitive games and other activities spread employees out over the entire picnic area, but a raffle at a predetermined time brings everyone back to one central location, encouraging camaraderie and excitement and re-energizing a tired crowd.
If you're soliciting donations from outside companies for raffle prizes, you are, technically, at their whim and should accept any product they offer. However, this doesn't mean you can't be fairly specific in describing the type of products you'd like. Keep your company atmosphere, employees' preferences, and local geography in mind. While younger employees may be excited to win sports equipment, briefcases may be more appreciated by older, more conservative employees.
Collecting raffle items takes time, so you'll want to start this step early in your planning. When soliciting for donations, approach companies you work with first--including sister companies--before reaching out to your larger community (try local record companies, newspapers, radio stations, wineries, toy stores, florists, music stores, garden shops, bath shops, manicurists, spas, golf courses, bicycle shops, sports shops, and banks).
Send a letter to the companies you're requesting raffle items from about 90 days prior to the picnic, and a second a month later. This will allow plenty of time for businesses to locate items, attain any necessary approvals, and send the items to you. In these letters, thank the businesses for any past support, let them know this years' event is coming up and that you're looking for universal or promo items that can be used by anyone (baseball tickets, concert tickets, limo rides, massages, restaurant certificates, t-shirts, artwork, savings bonds, autographed items).