What is the best food to eat for multiple meals a day?

I have heard that the best way to gain weight is to eat about 5 small meals a day, and was just wondering what are the best foods that should be eaten for these meals, and how much? I'm not big or anyting, I have just gained about 15lbs in a year and a half (was originally 98lbs, now I'm about 113lbs) and I would like to just get into shape, be fit and healthy. I do excersise often, I walk to work every day, I bike ride, go to the gym, swim, play frisbee, hike.. but nothing seems to stop my weight from slowly going up.. and was hoping the "5 small meals a day" may help, but not sure the best foods that should be eaten. If someone could tell me, taht would be great, and sooner the better if possible :-) Thanks