A good meal will change the atmosphere on a trip , I always have a secret stash of goodies for when things go wrong!
Generally trips involve physical excersise and you will eat more food than you do at home. People also have different metabolisms and may need to take food at regular intervals.
Food choices are determined both by the trip duration as well as by what type of activity you are doing.
Before the trip it is worth checking if anyone has any allergies, food preferences etc. If it's very complicated then let them arrange their own food but be aware that this increases the energy used in preparing it.
It is important that you use people experienced in that activity to organise the food - I have been on rafting and hiking trips that have had disastrous food produced by excellent chefs.
Unless you expect many portages or it is a longer trip, you can pack a fair bit into the rafts. Get dry ice for the cooler boxes and you can pack in fresh stuff as well (although you will be competing for space with beers if you are not careful). Food can easily be squashed on the rafts so packing in Robust waterproof containers is essential. As waterproofing is time consuming it's best to pack food meal per meal into clearly labelled plastic bags. This also helps to keep out the hungry hordes.
Water is not a problem on most rivers although generally it should be purified before use. There are lots of good systems out there but as a back up always take some chlorfloc. Water filters have a nasty habit of breaking so this simple fool proof system is worthwhile. The chlofloc both chlorinates the water and floculates it (in layman's terms the sand sinks to the bottom) This process takes 30mins minimum so do this in the evening filling all the water containers. Usually water that is to be boiled is not purified but goes straight onto the fire.
I favour an early start on the river so generally opt for cereal for breakfast and a light lunch with a big evening meal. It is useful to have lots of fruit and snacks throughout the day and these should be packed so that they are easily accessible