When traveling, bring one charge/sync cable for each device -- you never know when you need to juice more than one simultaneously. Retractable cables can save space, but they tend to break easily, so using rubber bands to corral traditional cables is a better idea.
In my backpack, I keep three charging/sync cables: one Lightning, one Dock, and one MicroUSB. That way, I can charge any device I may have -- as well as help out someone else who's in a pinch no matter what device they use.
Also bring a charger block that can power two devices; many do only one device, so you need more outlets and chargers. Be sure it supports tablets' higher wattage requirements on at least one port. If you rent cars a lot, get a second charger block that plugs into a cigarette lighter port. I like PowerGen's dual-port USB wall charger ($20) and its car charger ($30) due to their compact size, nice design, and reasonable prices.
I also now carry a portable rechargeable charger. You charge these via a USB cable, and thus have power ready should you not be near a wall outlet, such as on one of the many airlines and airport lobbies not yet providing in-seat power or at a conference room. I like the $18 PNY BD5200, which charges both tablets and smartphones (many of these portable chargers handle smartphones only). I also like the $39 credit-card-size TravelCard, but note that it doesn't charge tablets.