Pedals are important because the serve as the contact point between the rider and the bike’s transmission. Clip-less pedals systems come in a variety of designs favoured by individual manufacturers, but the mechanics of all styles are roughly the same. Tiny adjustments in the position of the show cleat – that snaps into position on the pedal – can make a big difference to the comfort and health of the rider.
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.
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.