Basic first aid supplies:  A few bandages of varying sizes.   6 Aspirin, or other OTC painkiller of choice.   A few alcohol pads in sealed foil packs, useful for cleaning grease off grease and grit off of the bike, and also cleaning cuts on yourself if you take a spill.  1 day supply of any prescription drugs you need to take regularly.   Wrap these up in tinfoil and tuck away.   It might just save your day.
2) On my second day, the pannier bag fell off and got lost after I stopped for lunch, which required locking up the bike somewhere, so I took the bag into restaurant and re-attached it using the two velcro straps on the rear rack. I've used many panniers before, thought I did it correctly. But apparently I did not. So I paid $55 (cost) to replace everything in bag and bag. In hindsight, I wished I'd put a bungee around bag straps to really secure it to bike. PROBABLY MY FAULT.
A pair of disposable latex gloves:  Not absolutely necessary, but good for keeping grease and grime off your hands during a repair.  Also, nice to have in an emergency when it starts raining and the temperature drops 20 degrees and you don’t have a pair of regular gloves.   Just keeping your hands dry and the wind from directly blowing on them makes a huge difference in comfort.

For the budding mechanic:  A good pocket sized repair guide.   One good option is the “Pocket Guide to Emergency Bicycle Repair”  by Ron Cordes and Eric Grove.   It’s only 3.5×4.5 inches and a half inch thick.   I don’t carry this myself, but for someone who’s new to this whole bike repair business, it’s really helpful to have. A future blog post will cover this book in detail.

Friction gear systems are a lot simpler to adjust, because the movement of the derailer cable can be modulated as you ride, every time you change the gear- they require less cycle maintenance. Modern index shifting systems are a little more complicated because each ‘click’ must release the exact right amount of cable to allow the derailer to move the correct distance to move the chain from one gear to another. Setting up and adjusting a derailer is not difficult and requires only basic tools, but there is a methodical procedure to follow.