"Recently" in the sense of "last year, but we're flying out again the day after tomorrow" ;)

Depends on the size of your backpack. I routinely use one of those conference-freebie rucksacks as a laptop bag and also as my hand luggage, so if you're thinking of something that sort of size, you should be fine (don't forget there are still restrictions on liquids etc.) From where, and with whom, are you flying?