One does not need a gift box - a big (transparent polyethylene even) bag of "apples" could serve as well, and indeed anything carryable, even a 1gal see-through plastic jug of "water". A radio set or a boombox, or a camcorder (like AQ did on Shah Masood), even a bike helmet - people with sufficient motivation will take time to mold and disguise their equipment into any benign shape. And now they picked an abominable clothing fashion of explosive vests and belts.
Make it a harder target. Guys who look like the 19 who pulled off 9-11 shouldn't be allowed to run around with huge explosive backpacks. Make it harder for them.
Don't forget big, thick, hollowed-out books.