The gap is closing between flash drives and portable hard drives, but for now, the latter still wins most of the time when it comes to price and capacity -- especially if you can find a good deal on one. Take Officeworks, which is currently selling Toshiba USB 3.0 1TB drives for $69, while the 2TB versions are $119.
Depending on your storage needs, you can probably do with a single drive, but just in case you need (a lot) more, Officeworks has a limit of ten per customer. Like all slim USB drives, there's no need for an external power cable and it weighs less than 200g, so it shouldn't be hard to carry around.
One thing to note is that Officeworks seems to have stuffed up the description:
It performs at a write speed of up to 13 Mb/s and a read speed of up to 21 Mb/s.
Ignoring that these numbers a listed in megabits (Mb) rather than bytes (MB), those are terrible speeds for a USB 3.0 hard drive and barring a defect, should perform significantly better.