Bikes are a great way to get around PDX, bike theft is a big problem. If you are smart about where you park and lock your bikes, odds are good that you'll return home with them. Park in sight of the streets, never in places where thieves have time and can't be seen. If you are careful and lock your bikes well you have the best chance. Make sure you have some insurance that covers the bikes, be covered if something happens, some peace of mind so you can have fun. Ask other bikers around for advice, you'll get good help that way. Water bottles, tool pouches, pumps are easy pickings, a small backpack is the place to keep these things.
Have a fun trip, it's a fun city!!