Mophie Powerstation XL lists for $129.95 but is currently discounted 42%, meaning you can pick this up for just $75 (See on Amazon). This ultra portable battery packs enough juice for up to 8 charges on most portable devices. It's special high-output battery can charge up to two devices simultaneously, and is capable of switching between 500mAh, 1A, and 2.1A charge.
At 2.8 x 0.9 x 4.5 inches, this item should be small enough for any traveller's accessory case.
Powerstation XL is currently rated 4.5 out of 5 stars on Amazon.com (222 reviews).