If you will be away from a pc and also be away from AC power, then you could use a USB battery pack to charge the Clip+. i have two of them, the Lenmar Powerport Mini, and the Tekkeon mp1550. The Poweport Mini has a built in lion battery and is itself charged via USB(either a pc or a USB wall charger). It is around the size of the Clip+, and has a 650 mah lion battery built in. I guess it might give around a full charge and a third to the Clip+? I paid $10 for my Powerport Mini.
The Tekkeon mp1550 uses AA batteries(2 or 4, but it will work much better with 4 than with 2.It will use alkalines or nimh batteries, however with alkalines the unit may become very hot and around half the power may be wasted as heat. It works very well with 4 nimh batteries, and will even charge nimh batteries inside the device via USB(it takes around 6 hours though). The Tekkeon mp1550 is around $20. It might be able to get around 7 full charges of the Clip+ using 4 2900 mah nimh batteries?
Another interesting USB charger is the Tekkeon mp1800. It has a 4,000 mah lion battery built in. It might give around 8 full charges of the battery in the Clip+? It is around $35.
Duracell also makes some USB chargers with a lion battery built in. The Tekkeon chargers seem like better values though.