If you've got a floor lamp or guitar stand - assuming you haven't got wall hooks, which are great for keeping guitars safe - you can get a pick clip; they're designed for mic stands, but they're great for keeping the random ones normally lurking in bags, every pocket, top of the washing machine, in the washing machine, in the sofa, under the sofa, under the cat bowl, in the cat's bed... (I have an adult Guitar Twat in the house) it means there's always a pick to hand and somewhere to put them. Capos just hook over the guitar stand or you make them learn barre chords.
9v batteries go in the guitar cases with spare strings - with all manner of misfortune threatened if they put the exhausted ones back in the case, but make sure they're left wrapped or in the box, as you don't want a capo completing a circuit. Other batteries need to be hidden away from 'I just needed another one for my tuner'.
Cycle helmets hang on handlebars/around the crossbar - no excuse for forgetting or losing them that way.
Gumshields go back in the case and into the sports bag with the shinpads as soon as they're clean so they can't be forgotten.
The key is finding a place where they are used, normally found and/or transported, not where a special trip a whole nine foot away is required.