Otherwise, this tool should serve the average commuter well. Specifically, we think you’ll find the size 4, 5, and 6 hex keys, extremely common sizes in bicycles, very helpful. They’ll adjust seat-post heights or let you remove the saddle entirely, or tighten a loose stem that’s always rattling apart. The Phillips head will tighten loose bolts on shoe cleats or the rear derailleur. The most common use for the torx would be adjusting disc brakes if you have ’em.
In addition to the Rema patches, put a new tire tube in your kit. The best method for dealing with a flat roadside is to swap out the tube and save the task of patching for later. If you’re not sure what size your tires are, it’s printed on the sidewall of the tire. This inner-tube buying guide has some photos of where to look. What brand is almost irrelevant as many tubes get manufactured in the same place, so whatever your local shop has behind the counter for under $10 will work fine. The only reason to spend more would be to save weight.
There are patches that don’t require vulcanizer—the infamous peel-and-stick. One brand, the Park Tool GP-2, has some genuinely enthusiastic endorsements, so we tested it. I applied Park Tool patches to four different tires, at three different psi levels (60, 90, and 120). Three of the four didn’t hold—two released within minutes. The fourth deflated overnight. I redid the test, but repeated a second time, they all leaked within a day.
Any bike that gets ridden seriously as transportation or on long rides needs at least a basic tool/emergency kit, and the knowledge to use it, unless the rider is always in a position to call a friend with a car or a cab when their bike needs a quick fix on the road.  If you never travel more than a few miles, this can be overkill, and calling a friend or a cab may be just the ticket,  but if you want to be more self reliant, this is something you should seriously consider.  This list may sound like an awful lot of stuff to carry, but really, it only weighs a few lbs and fits in a small, under-seat bag that comes off quickly so I don’t have to leave it with the bike if theft is a concern.  If you always carry a regular rack top bag, you can also just put all this in a small nylon bag and throw it in there, but I prefer an under-seat bag.

These are some great ideas, especially the simple ones like bringing a garbage bag. That’s something so easy and cheap that it’s easy to forget entirely, but as you say, it can make a huge difference in the right circumstances. It’s also good that you discuss some minor bike repairs. That’s another thing that can salvage or destroy your ride. You want to be as prepared as possible for the best possible experience.
Modern bottom brackets use a sealed bearing type construction that keeps water and debris locked out, so they seldom go wrong. Maintenance is impossible so they need replacing when they do wear out. Older style cup bottom brackets need to be re-greased every now and again, and occasionally will need to have their bearings replaced. There are a lot more teeth on the chainring cogs than those on the rear cassette, so need changing less regularly. Cranks usually a solid one piece construction so there is not much to go wrong.
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