I agree that making a table runner or pot holders to coordinate with the dishes or pots they're registered for could be a good solution. Honestly, I'd say most young couples I encounter are not big on placemats, etc. However, you could try looking up the bride's name on Pinterest (What bride doesn't have an account?) and get a sense of what her style is. If you saw a lot of handmade/quilty types of things, then you could feel pretty safe in making a nice throw sized quilt or throw pillows.