^ Repetition is the only reliable solution for me - I go to the supermarket about every third day or so, and I buy exactly the same items every time, bar the odd "once a month" thing like washing powder or loo roll. If they move the products around the store or stop stocking something that I usually get, it can easily fluster me enough that I just have to leave, or I turn into an immobile obstacle for a while. I've tried using lists, but it doesn't really help. Lists only tell me what I want to get, which I know well enough already; it's the activity of shopping in and of itself that's the problem - and it only goes smoothly if I can do it like an automaton, minimising my awareness of the environment.
I'm well aware that this way of doing it makes my diet very repetitive, and that there are consequences for my health of this; but it's better than going hungry. I'd use internet shopping, but I figure that going on foot is a fair trade, as it forces me to get out into the world and get some exercise that I might otherwise avoid.
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When you are fighting an invisible monster, first throw a bucket of paint over it.