Make a master list of all the items that you may want to take with you... anything from a tin-opener to guide books, spare batteries etc.,etc. Refer to it each time that you load up for a trip (maybe print out a new copy each time) and tick off each item. After each trip you can add to the list, or remove items that you can live without.
This will save any worries about forgetting to take something important, and may also save packing any surplus clutter on future trips.