Whenever I go out for photos, I also pack a travel kit, which is part of the supplies I like to have for short or long-term travel, with or without my camera. I usually have it right in my backpack at all times:
This kit provides me with stuff that I've found over the years, I like to have with me. Some of it is for emergencies (coffee, spare sunglasses, or first aid information). Some of it I use often (sunblock and hand sanitizer). Other items are for convenience, like a pen, a toothbrush (in case of an unexpected stay somewhere overnight).
Packed, the kit looks like this: