Placing items that will be least used — or used last — at the bottom of your suitcase or bag will help eliminate “bag rummage.” Think of the order in which you’ll use items and pack accordingly. Items used frequently or that will be used the soonest should be packed near the top.
When packing small items, pack them in containers inside luggage so they don’t end up at the bottom of your bag.
[Ed’s not: this is useful for carry-on luggage, as well. You don’t want to be digging through your day bag trying to find a pen to fill out the immigration card.]