2. A/C USB charger, one or two port. This lets you charge your USB devices from a wall outlet.
3. Phone/PDA accessories.
Phone/Smartphone batteries may not last all day, especially if you're doing a lot of online activity, or using them as a WiFi hotspot.
a) A/C charger, if you don't have a USB cable/charger combination -- or if the regular A/C charger works significantly faster. Look for a "travel" charger that's more compact, but make sure it charges the phone quickly enough.
b) Portable power pack, for when you can't get to a wall outlet -- along with whatever cables you need to connect to the device, and to recharge the pack.
Duracell, Energizer and others sell sealed rechargeable power packs as well as ones that use two or four AA cells. Some have built-in cables. The sealed ones are smaller; the AA-based ones let you use drug store batteries for the recharge.
4. Camera/video accessories.
I recommend packing a spare, charged battery. In normal use, today's camera batteries last all day, but if you didn't recharge, or you're shooting video, you may need that spare.
Also, a spare, empty media card -- again, video chews through megabytes quickly.
Charging/data cables, if the USB ones you're already packing aren't sufficient.
5. Other mobile accessories
a) USB media card reader (for SD, micro-SD, CF, etc.). Even if you can download your pictures using the data cable, a small one can't hurt to have.
b) An extra media card or two for each device.
c) An empty USB flash drive or two - a 4-6GB for you, some 2GB's or under in case you need to give one to somebody.
d) Battery charger(s): Unless your device (e.g., a camera) can recharge them via its USB cable.
For the batteries in your mobile devices, Vivitar and others offer "universal" chargers... just test ahead of time to confirm they fit and charge the batteries for your phone, camera, and whatever else.
If you use AA or AAA cells (like in a Cisco Flip, or a handheld audio recorder): Duracell, Energizer and others make chargers that will fill up their brand of batteries in 15 minutes... but these chargers may be more bulky and heavy than you want to deal with, in which case, look at Duracell's and Energizer's more compact chargers that can still do the trick in a few hours.
6. Notebook accessories. Here's where your kit can start bulking up.
a) Bring an A/C charger. Targus, Antec and others make small, lightweight ones, many of which also have a USB charging port and/or secondary charging cable for mobile device. Don't forget to bring the necessary tip(s).
b) Ethernet cable, and, advises mobile veteran Chris De Herrera, an Ethernet coupler, so you can use your cables to extend one that's there into one longer one.