If you are having your wedding reception outdoors, then that opens the door for many activities that would be hard to pull off indoors. You can plan games and activities based on the outdoor theme and carry that theme indoors if part of the reception is inside as well. Depending on where the reception will be held, you can plan many activities based on the setting. Whether it is the park or on a farm, there are a myriad of activities you can plan.
Let's start with some basics based on popular wedding locations. One fun game for a winery wedding is a blindfolded wine tasting game. If the bride and groom are wine drinkers, this might not a game the bride and groom should be a part of, but instead guests and wedding party members. Blindfold perhaps a half dozen volunteers and have them do a blind taste test (provide something to clean the palate between sips). The volunteers should guess which wine is the pinot noir, which is the Cabernet, and so on. A bottle of wine is the obvious prize for the winner of this game.
Say you are having a reception at a country club on a golf course. It's possible your theme will include golf elements, so why not include golf in some reception activities or games? You certainly could head to the golf course for a "hole in one" contest, or have a driving contest to see which guest has the best stroke. As a simple, "who gets the centerpiece game", you could have people guess how many golf balls there are in the floral centerpiece (which could decorate a plain large glass vase filled with flowers). Similarly, there could be a large vase or other clear container filled with golf balls at the reception somewhere and guests could guess how many golf balls are in the vase.
A silly game could be made on the dance floor by asking everyone to include their best golf swing into their dancing for one particular song.