Most of the resort gift shops have a pin trading board. And the concierge's have books. Ask if you don't see one visible. Some of them are downright terrible. Some do a better job of refreshing.
For hopping, it's easiest to do it if you start at a park close to a specific resort. So if you want to go to Animal Kingdom Lodge, get a bus from Animal Kingdom, not one of the other parks.
MK: Monorail loop hotels, boat to Wilderness Lodge or Ft Wilderness
Epcot: bus to Caribbean Beach, Port Orleans, boats to Epcot lagoon hotels
Studios: also boats to the Epcot lagoon hotels, Coronado Springs, Art of Animation, Pop Century
AK: Animal Kingdom Lodge, All-Stars
Downtown Disney: Caribbean Beach wouldn't be horrible, but there is also a boat that goes to Port Orleans, that's a nice little thing to do.
DVC resorts like Old Key West, it's easiest just to drive. You can walk to Saratoga Springs from Downtown Disney, but its a bit of a walk.
If you do just choose to drive, they will ask to see your ID at the shacks when you enter the resort. The easiest thing is to just tell them you are getting something to eat. They'll tell you where to park, and wave you through with the least amount of hassle.