Gaps in wall, near ceiling, how can I fix it?

Go to your local hardware store and get some insulation meant for gaps. It looks like a round tube of foam about 1/2 inch in diameter. Cut pieces to fit the gaps and then caulk. This should cost you less than $10 and take less than a half hour. You may have to borrow a caulk gun if you don't have one or don't want to buy one.