Patch kit: Patch kits are easy to use, light and compact, and if you get more than one flat on a ride (it happens more than you’d expect), it can save you when you’ve already used your spare tube. Plus, on a rear wheel, patching a tube can be faster than replacing it, as you can often do this without removing the wheel at all. Another upcoming post is going to show you how to patch a tube.
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.
Spare tube: Sometimes, a tube is just too damaged to be patched, or has had a failure such as the valve stem breaking off which isn’t something that can be patched. To save weight and space, I usually keep a lightweight version of the right size tube for my bike. Since one of the first things I do with most bikes that I own is switch them over to heavy-duty thorn resistant tubes, I just take one of the originals and put that in the toolkit.
The fabric attachment system is low-tech, but that seems to be helpful, as it can adapt to seat rails of different widths. One fancier option you might see on more expensive seat bags is a quick-release mount that you install under your saddle. But those have a fixed width, and therefore can fit under seats with only those exact specs. Brooks saddles, for example, are too wide for these mounts.