Battery packs are a must.
I use a 12V/2.3Ah three-cell Li-poly battery, sourced from China in quantity as part of another project (sequesterde a pair for myself) as the main power pack. This gives me 12 volts on a bog-standard 2.1/5.5mm barrel jack. Useful for 12V gadgets, e.g. a miniature soldering iron.
Then there is a modded car lighter-plug buck converter, having the barrel jack as input and providing two USB-A sockets (and one short stub of a microUSB cable). That provides me with 5 volts for smartphone (earlier it was a Nokia E71 modded with microUSB charging connector in addition to the stock one), camera (a modded Nikon so it has a microUSB for charging, a 3.5mm jack for audio/video output, and another microUSB for data upload, instead of its proprietary crap), a modded ebook reader (with microUSB for charging), and other USB-powered gadgets. Up to three things can be charged simultaneously, one with the stub cable and two with regular microUSB cables. The charger assembly then comfortably fits in a thigh pocket of cargo pants, and the long wire assures comfortable use of whatever peripheral is in operation.
Modular design, with good six times the juice the overpriced off-the-shelf stuff provides. (Three times each, two batteries.)
For charging the batteries, a microprocessor controlled aircraft-model grade charger is used; an overkill but that's what I have. (Todo: Get or make a smaller one.) Modded to use a laptop power supply (with a switch with four silicon diodes (0.7V loss on each) to drop the 19-20V voltage to below 18V where the charger stops complaining about overvoltage). The laptop PSU itself has an adapter from the IBM socket (harvested from an old laptop, sticking to one brand has its advantages as over the years you accumulate a stockpile of spare parts) to the barrel jack, tied to the cord to not get lost.)
European airports so far cope with the wire ratsnest fairly well, seems to be a matter of pro-looking casing.
The Spring thingy is clever. Should try it out with Sugru. Would be compatible with way more earphone models than with just The Fruit. The Smartwrap thingy as well, but not $5-a-piece clever, when the same can be lasercut (or even handcut) from an elastomer sheet or hand-moulded from Sugru.
A lot of hacks can be done on the go. In addition to Sugru (good material but with annoyingly long cure time when you're on the go), a good stuff to carry is a little bag of polycaprolactone (aka Shapeloc) pellets. It was in a hotel room where I used hot water from a tea kettle to shape a connector strain relief overmould from this material, to get me out of trouble. (Add a microsized soldering iron with a small spool of reliable lead-tin solder, some heat-shrink pieces, and couple other tools and you get a pound worth of stuff to keep your electronics healthy and happy.) So polycaprolactone should go to the gadgets list too. Maybe a separate repair/mod-things-on-the-go list too.