In reply to Ns1234:
Is this a school project? It sounds a bit like it.
As for the actual question, a rucksack-carrying drone* or lots of helium balloons. Alternatively, take a slightly wider view of the problem and ask yourself what you are trying to carry and whether there's a better way of doing it, not necessarily involving a rucksack?
(*These already exist. Yaks, donkeys, camels or courier companies, depending on whereabouts in the world you happen to be.)