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.
Be organized. “I like having everything be really small and super organized. I put all of my tools in CamelBak’s Tool Roll. It’s got little compartments, and I can separate tire changing stuff in one place, stuff like extra pedal cleats or an extra derailleur hanger in another, and it all rolls up into this tidy pouch. If I do have a repair, I can pull that one thing out and lay it out on the ground and it’s easy to work.”
Change and a $20 bill:   In case your cell phone’s battery dies, it’s nice to still be able to use a payphone if you need to.   Also, the $20 is a great thing to have in case you lose your wallet or have some other mishap.   I’d rather be able to sit in a coffee shop or fast food restaurant when it starts raining while I’m waiting for my friend or cab ride, and a hot cup of tea or coffee or the beverage of your choice and a snack makes it all the more pleasant.  Just try to remember, this is for emergencies, and if you use it, replace it ASAP!

I bicycle to and from work to save gas. I don't have a fancy bike, it's just a Schwinn mountain bike that's comfortable and can carry me plus gear but I want to be able to do my own work on it. I needed a book that was simple enough for someone new to bicycle repair and maintenance but could take me through all the upkeep my workhorse needs, and this book does just that. It's well-written and easy to follow.

If you are planning on going on a multi-day ride or just riding a long distance in a day, you should have something for first aid, just in case. Unfortunately, almost everyone who cycles frequently will go down at least once in their life. This kit can be really small and compact and can include bandages, some gauze, and a small bottle of a disinfectant.

These folks took me in right away, diagnosed and fixed my stripped handle bar clamps and had me on my way to work in about 15 minutes. Friendly, straightforward, understands the rider's objectives (in my case, how do I get home from work). Not to mention, the fee was reasonable. I have been in many bike repair places in my 6 decades. This is the best.
If you’re going to use the chain whip you just made, you’ll also need a way to get that cassette off. A lockring remover is a must-have; unless you use one of the shady removal methods I’ve seen on the internet—which I wouldn’t necessarily recommend unless you don’t care much about the condition of the wheel after you use them. I recommend Park Tool’s iterations here that cost about $6, but you’ll need to buy the specific one for your brand/type of cassette. (By the way, I’m assuming you already have an adjustable wrench laying around somewhere to use with this tool. If you don’t, well, you’ll need one of those too.)
Man, if you're starting out and you know you'll need several components for a bag... just get this. It will save you so much time picking everything out that even if you balk at the price (amazing value, by the way) I bet that if you did the math using your hourly wage and the time spent picking everything out and making sure it fits... you'd save a lot of money and a lot of irritation if you just got this. Just get this.
Dennis Bailey has been actively involved in bike repair and maintenance for almost two decades. He has worked on bikes on bike tours in the United States, Europe, and Latin America. Keith Gates has been repairing bikes for more than 30 years and provides personalized service as the owner of A-1 Cycling, with locations in Manassas and Herndon, Virginia.
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.