Beverages
Water. It can save your ceremony and reception. If your ceremony and reception will be outdoors on a hot, sunny day be sure to have plenty of water for your guests to drink. Even with shade available, dehydration is a possibility.
Water is also a great alternative for your guests who don't drink alcohol or avoid soda. Tea and lemonade are also refreshing but if you are not making the lemonade yourself at least get a taste test from the venue. I swear, one venue passing a canister of lemonade mix over the pitcher, puts in just enough to discolor the water and calls it lemonade.
Alcohol. Proper etiquette says if serving alcohol you must have an open bar. I say horsefeathers! Certainly, if you have the money and the desire, by all means have an open bar. But if you are concerned that some guests might over imbibe or if you are on a tight budget this is one place you can save money. Options include having a signature drink that is hosted, an open bar only during the cocktail hour, hosted wine and beer, or have your reception in a facility that has a bar on premises but you do not have a bar actually set up in your room.
Also, have some designated drivers or make other arrangements in the event that some of your guests do become inebriated.
Coffee. Even if you don't drink coffee some of your guests probably do and would love a cup after dinner or with their wedding cake. Consider having a pot available but it doesn't need to be gallons of coffee.