I think you can use existing software to do that. If your store has wifi (even if you can't access it, I think), you can geofence an area and have some action (such as popping up a reminder app) trigger. I've not used software like this myself, but I remember people describing behavior like this at least on Android. If it might be useful to you, you should give it a search.
I have an app that's meant to schedule things, but I just use it as a checklist and preface each action with the location. So long as I check it (second home screen on my phone, so not a huge barrier), I'm usually good.