My understanding is that bank would generally have title to the permanent fixtures in the home, and that the prior homeowner would have the right to keep temporary fixtures, decor, and other personal property. Most things are clear-cut: a toilet is a permanent fixture. A shower curtain is not.
For some items that aren't so clear-cut, it depends on the way things are handled in your jurisdiction. In some areas, appliances like washer/dryer/fridge are traditionally bought and sold with the house. In those areas, those appliances would be considered permanent fixtures of the property. In other areas, the appliances don't usually convey with the house, so they wouldn't become the bank's property either.
Many people make improvements like upgrading shower heads, adding a chandelier, or installing fancy light socket covers. You're probably within your rights to take those back as long as you install a replacement, and those replacements don't have to be very nice.
It's sadly become common for homeowners to strip a home that's in foreclosure, taking permanent fixtures when they leave. Those items are technically your property until the place is actually foreclosed. If you happen to sell your fridge on Craigslist for $200, there's not much your bank can do.
After foreclosure, the new owner's top priority will be to get you out of the house quickly and quietly. I've heard that they'll actually offer cash for cooperation, so that the resident can leave with some dignity and have some cash to start a new life. The bank isn't going to go after you for the curtains -- it's relatively unimportant, it's not worth their time, and you probably wouldn't be able to pay them back anyway.
Disclaimer: I'm not a lawyer nor an accountant. Everything I just said is probably wrong. :) I learned all of this last year when I bought a house that had been foreclosed and was "stripped" by the previous owner.