When putting down an object that you will want to leave a given area with make a strong mental note of its placement and rehearse that note periodically so that it will enter your mind to pick the object up and carry it on your person when you leave. Preferably, put it with your pack, in a pocket, or somewhere else where things you will very likely remember (or not have to remember, as in the case of pockets) to leave with are concentrated rather than leaving it somewhere by itself.
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