one for the outer door, two for the inner, three for girlfriends place, one for the office, one for the postbox, one for my bicycle, the car, the motorbike and the roof
Go buy a carabiner. Spend more than $10, preferably climbing grade. Cheap ones will break or the cheap coating will rub and stain your clothes.
Buy 3 key rings:
Ring 1: Outer Door, Inner Door, POBox, Main mode of transport and office
Ring 2: GF keys
Ring 3: Roof, Secondary modes of transport
Buy a key rack and keep ring 2 and 3 there. When you need them, clip them. The biner will make adding / removing sets of keys easy. You can clip it to your belt, pack, bike, etc. After a bit, you will get used to the weight and not having it will remind you to grab them. As the number of rings grows, you can tag / color code them for easy reference.
"Floggings will continue until morale improves." -- anonymous flyer being distributed at Exxon USA