Lots of talk on here about surgical tools and other replacements for third/fourth hand tools. I use vise-grips. Clamp it on to the brake cable, use one hand to close the brakes (weight of vise grips pulls cable somewhat taut -- be aware of where the vise grips will move if you are worried about banging your fork/frame) and I have a hand free to tighten the bolt. Also, if I tighten too far, then I clamp the vise grips onto the cable with a 2-3mm gap to the pinch bolt, loosen the bolt, let the brakes expand to meet the vise grips, and tighten again.
Has your youngest child outgrown the family crib?
Make yourself a bike rack! Mine is currently holding all 9 of my family's bikes. (Well, 8 right now because I have one at work with me)
Speaking of homemade bike racks, why spend $$$ for Thule/Yakima specialty bike trays? You've already laid out long green for the towers and maybe even crossbars (unless you made cheap crossbars from the advice above), so why not make yourself a roof-rack or two
like this? It's strong enough that you can pull the frame and rock the car. And note I destroyed a bike (thankfully a cheap MTB from CL) that was in this thing by plowing (slowly) into a balcony. The fork was spaghetti, the thule crossbar was bent, the thule clamp was bent, my honda oddyssey roof-rail fairing was cracked, but this little rack came out unscathed!
Have you recently fixed/adjusted some part of your bike?
Take the corresponding tool(s) on your next ride, in case you jacked it up and need to fix it on the road. (I liked that guy way back that used a guitar pick to remove a busted FD -- I could have used something like that!)
Somebody up there said about using egg cartons to hold a variety of small parts; that gave me the idea of using an egg carton to keep small parts in order, like if you take off spherical-washer brake pads. Of course there's always zip-tie or twist-tie. (If you have kids or grandkids, at Christmas time grab up all the plastic-coated metal twist ties used in toy packaging nowadays -- that stuff is strong and long (that's what she said!))
Another idea I recently had but haven't tried yet. If you use chain-L and really want it to get deep in there, empty your bottle into a tough gallon ziploc bag, and let your chain marinate overnight. Or for months, if you are a multi-chain-rotator. You'd also have to hang the chain above the open bag for quite a while to recover all the extra lube. Or maybe not the best idea, as you'll contaminate your entire supply of Chain-L -- unless that is just your new-chain treatment.
A few people have mentioned I think
SB's homebrew BB fixed cup tool, but I'm not sure anybody mentioned you can make a similar headset press out of a long 1/2" bolt and nut and stack of washers. And somewhere on BF a while ago I saw
Dave Moulton's cool homemade headset extractor made simply by splitting some copper pipe.
I think my number one tip/trick is the principle -- don't buy bike when you can buy generic. Anything custom-marketed to the bicycle market is crazy expensive. For instance, instead of a bike light with a custom handlebar clamp, I use a badass 1600 lumen (allegedly) CREE LED chinese-made flashlight I got for about $25, held rock-solid with two interlocked hose clamps. I don't think I can get that much lighting in a "bike light" unless I get up into the triple digits. Also,
from BF advice, I hacked (er, custom fabricated) a bracket to mount my rear blinkie onto my rack, out of plumber's metal tape (used for holding up long stretches of pipe, or strapping water heaters to studs as per CA earthquake safety regs).
Speaking of metal tape, I also had a problem where I was using a seatpost rack and my pannier straps couldn't reach all the way down to the dropouts to hook into the threaded rack hole. Bolting in a few inches of metal tape though (folded over for double-strength), hook the straps into the top hole of the tape and cinch them down tight, and that seatpost rack becomes as good as a full rack.