I live somewhere where it usually gets down to freezing sometime in the winter, but not for too long, and we never get snow. Lots and lots of rain, though.
- money for a cab or bus (or bus pass and payment card for taxi)
- ID card (but thinking might replace or supplement with road ID)
- lights if darkness is likely (I have a front and rear reelight set that stay on, but if darkness is at all likely I'll bring a real headlight and tail light, too)
- pump (it's attached to the bike)
- water bottle (in cage)
- small U-bolt lock (mounted on bike) unless absolutely sure I won't be needing to lock up.
- cell phone (turned off for long recreational ride through poor coverage zones; on and in pocket for commute)
- wearing clothes that are chilly to stand still in but comfortable for riding in after about 5 minutes
- house key and u-bolt lock key
Most of this attaches to the bike, the rest can fit in an under-the-saddle bag or some other kind of small bag attached to the bike. This is what I'd bring for a recreational ride anytime of year. So no actual pack.
Try to add to minimum, but don't always:
- tire levers
- spare tube and/or some patches
Yes, if it's really cold outside it can be hard to patch. Been lucky enough not to get a flat when it was that cold, but thinking I could still figure out how to get a flat dealt with wearing gloves (for part of it?), alternating between working on flat and sticking hands under clothes, or convincing a store to let me in, or with slow leak some repeated tire pumping to get somewhere and then fix flat... Even huddling on the leeward side of an embankment would make a big difference
- Absolute minimum set, plus:
- wallet (money, ID, medical insurance card, a couple payment cards, etc)
- either a pannier that attaches to rack, or a small messenger bag that I'll bungee to the rack. Sometimes carry the small messenger bag, especially if it's dark out, since it's got retroreflective stuff and makes the rear blinky slightly less visible
- One or two "chico bags" (nylon bag the size of a plastic grocery bag that folds up into itself to a size smaller than a tennis ball). If I stop in a store these are easier to jury-rig attach to rack with bungee cords than a typical grocery bag.
- 1 spare tube inside of a sock
- patches (in case of two flats)
- multitool (that includes tire levers, several sizes of allen tool, chain tool, several sizes of wrench, screwdriver, knife)
- some kind of snack (energy bar, granola bar, chocolate bar)
- rain jacket (almost every day during the 5 months of wet season)
- rain pants if there's any possibility of rain (I check first)
- reflective ankle strap if bringing rain pants
- case for sunglasses, which includes alternate lens color choices
- scarf and wool cap (wool) if there's any chance of temp getting below 50F (10C)
- If warm: normal fingerless cycling gloves with mesh back, padding on palm, etc
- If cold: some wool fingerless gloves
- If freezing cold: full-fingered wool gloves
- hoody/sweatshirt/sweater/jumper/light jacket if temp below 40F (5C) or likely to drop below freezing
- a bungee cord or two. maybe a cargo net.
- cable (attached to lock) for securing wheel
- bottle opener (it's on usual keyring, works as a prytool, flat screwdriver and a few sizes of metric wrench, too)
- work keys (either because riding to/from work, or because easier to just leave on keyring)
- all the rest, plus
- Spare batteries for lights. (battery for cell phone if I had it; keep meaning to get one of those)
- second multitool (different type, selection of bits including a bunch of allen bits, better knife, easier to do some stuff with this)
- travel mug with some kind of hot beverage
- second water bottle in that hard to reach cage (I have 3 cages total). Possibly with some sort of beverage with a bit of sugar, like some watered down lemonade.
- snack selection (or even a full lunch if timing looks right). usual bar-shaped foods, fruit, salame, some cut veggies, whatever I felt like putting together...
- one of the other sets of gloves (a bit chilly now, so wear fingerless wool gloves, but might be riding home really cold so also bring full-fingered gloves)
- a small towel if any chance of rain (dry off face and maybe hands if they get rained on)