I don't have time to read all the posts so I'm sure all of what I'll mention has already been said, but to start, say no to electrical tape, say yes to black Gorilla tape, it's much tougher and more useful then even duct tape.
For small loose stuff you can make a Altoids tin to carry that stuff and put it in the saddlebag, I made my from this idea but customized it for my needs:
http://www.instructables.com/id/Bycicle-Survival-Kit-/ In that tin 2 layers of about 1/16ths of inch thick foam padding I cut to size of the tin. On the bottom of the tin I put butterfly stitches, bandaids, $50 in bills, 50 cents in quarters, I then put one of the foam pads on top of that, then Park glueless boot patches go on top of that foam pad, then I cut one of the pads into an L shape so that the cut out section fits 2 Park Glueless patch boxes side by side and place that pad on top of the previous pad, then I fit in the Park Glueless patch boxes, one with the patches and the other I put pills in for diarrhea, benadryl, sinus headache pills, and ibuprofen (logic will tell you why I carry those pills, and I throw out the old and put in new at the start of every season). On top of that last L shaped pad I have an extra computer battery, schrader to presta converter, house key, and bike lock key (though I don't always carry my lock it's just in there for when I do). I then glued a state ID card to the inside of the tin lid.
I have a Topeak Aero Wedge bag, the tin fits nicely into the web restraint on the lid of the bag. In the bag I carry a spare tube rolled tightly and held with a rubber band in a ziplock bag, Park MTB 3 multi tool, cheap pair of folding pliers, a VAR tire lever, a set of Soma Steel Core tire levers rubberbanded together, 4 alcohol pads (for cleaning the tube after sanding it for a patch, and for cleaning road rash), 2 lens cleaning pads, and 4 handwipe toweletes (you can get these for free at certain resturants, they're great for cleaning your hands after fixing a flat or mechanical problem), and paper towels in case of needing to take a dump in the wild (paper towels last longer in a seat bag then toilet paper does), 4 short zip ties, on long rides or tours I put a meal replacement bar in the bag, and when I do a weekend tour I throw in 2 FiberSpokes, and finally my cell phone sometimes!
I don't carry a spare chain link because if you break a chain you can take out the broken link and put the chain back together minus a link or two, the only problem you'll have doing that is you might not be able to go into your smallest or your largest sprocket but otherwise you can ride like normal. I also don't carry a 2 spare tubes, I can repair a hole in a tube and be on the road in the same time it takes me to replace the tube, so why bother? I don't throw out a tube because I got a puncture, I fix it, and there's no reason to take up that sort of space in a seat bag for 2 tubes unless you're not proficient at fixing a tube. You're probably wondering how I can fix a flat in a tube faster then replacing the tube. First off most punctures I can find quickly from eyeballing the tread, once it is found I leave the whole wheel on the bike, I don't take it off, I take off about half of one side of the tire bead with the puncture in the middle, I then pull out about a quarter of the tube with the puncture in the middle, prep the hole to accept the glueless patch and patch, I then pull out the thing that punctured my tire, replace the tube and put the tire back on, pump and go. I don't have to worry about putting the wheel back on, I don't have to wait for glue to dry, I don't have to roll up a flatted tube letting air out as I go so it will fit in the bag. I also don't carry CO2 because I don't like the idea of buying air that I can get for free, I also don't like the idea of going home and taking all the CO2 out of the tube and refilling with air...why do the same work twice? Where's the time savings in that? Besides I'm not racing so I don't need to get to the finish line. I also don't like the waste of the product, in fact I actually hate cyclists for using CO2 because most of those primates throw their used CO2's on the side of the road!
On the subject of glueless patches, a lot of people don't like them but I have had only 3 glueless patches fail in over 20 years of using them, one was my first attempt, the other 2 were cheap Skab or somesuch name patches that wouldn't stick, after that I only bought Park or Specialized Fatboy patches, lezyne supposedly makes a great glueless patch too but I haven't tried those. If the tube is properly prepped the glueless patch will hold for the life of the tube.
I rarely have a mechanical issue on the road, in fact as weird as this sounds, in over 40 years of riding I have had only 1 mechanical issue, why not more you scream? Because I am very meticulous about checking my bikes over before and after every ride, I keep my bikes clean and lubed too, I catch almost all things before they lead to a breakdown. The one break down I had wasn't major, a headset on an older bike came loose, I tightened by hand since I had nothing that size in my bag to tighten it with, I rode the bike to a bike shop and they fixed for free but I gave them a $20 tip!
Of course the final tool is the mini pump, get a good one, most mini pumps will not reach the psi you want to put in the tire, the one I like the most is the Lezyne Road Drive large size, the other 2 sizes makes your work harder and I doubt if the small one will get to the psi you need, the medium I heard will but your work will be harder with it. There are 2 or 3 others that are also good like the Topeak Racerocket HP will but it's more difficult to use at higher psi then the Lezyne; next one is the Topeak Road Morph G though technically this one is not a mini, it's a half frame pump, it works the best of any mini, but it's ungainly looking; next one is the Airace Mini Veloce, not quite as good as the Lezyne more on the lines of the Topeak Racerocket HP. There maybe one or two more but I don't know what those would be. I own all those pumps except for the Airace which I'm considering buying one just to try it out, besides I need another one anyways!
