In the end you might want to get some extra memory cards, they take less space and weight in your lugage as any hdd solution.
and using multiple cards also helps to spread the risk of data loss... Better to have one corrupt 8Gb card as a 120Gb drive
If you own an iphone or samsung there are some camera connector kits out there which you can use to store photos on your phone, but be aware importing in apple might result in screwing up the jpeg to make it apple compliant, test drive that first please.
Olympus: E-3, 12-60SWD, EX25,EC20, FL50R, 50-200SWD, XZ-2.
Thinktank: Rotation 360, Change Up, some modules