I used one as a laptop etc. bag for a long time. As laptops got a bit smaller I now tend to repurpose a Mountainsmith bag (used over the shoulder) these days as my travel "personal item." But, in any case, some sort of shoulder bag is my goto. I find there are some downsides to backpacks on public transit, etc. and I end up with them slung over one shoulder anyway so why not use something designed for that usage.