Most general items can be carried and stored in your main bag, but a lockable day pack/bag is essential for those items required during the day. Try to keep your luggage to a minimum, and remember to keep to your airline's weight restriction (normally 20kg or less). Note some tours have luggage weight limits - check your tour dossier.
Your luggage will be dependent on the type of trip you are taking, but a holdall, a soft bag on wheels or a rucksack are ideal for adventure travel when luggage is carried in vehicles. As a rule, hard cases should only be used on centre based trips (ie. dive tours or city stays). Your tour dossier has advice on luggage type.