@Linkat,
Oops!
Sorry if my backpack hit you. In defense of myself, I tend not to carry a great amount when riding the subways. A couple of half liter bottles of water, some reading material, a couple of pens and small pad of paper. Also some paper towels and tissues, as well as several lifesavers mints.
That covers going someplace. If I make a purchase, it is usually small and if it's too large, I opt for a cab.
Taking it off, for me is a little difficult as I walk with a cane and have limited arm dexterity. When traveling with someone, I often ask them for help in removal of the backpack when boarding transportation.