Hi J.-
For the constipation I agree with the mom who wrote about the 'P' fruits- prunes, plums, peaches. You could always try a couple ounces of prune juice. Bananas, applesauce, cheese- try to limit these as they have a tendency to be more binding. You might also try yogurt to keep him regular-Stonyfield's Yo-Baby is great.
As for lunches, you could give him yogurt & soft fruits. Check with the doctor, but since he is almost 1, you might even be able to start him on peanut butter & jelly cut into bite size pieces. Also, if the doctor okays it you could try fish. Tuna is easy, but not more than once every week or two because of mercury levels. You could also try meatballs- without sauce & cut into small pieces- or meatloaf. My 9 month old eats these without any problems.
Even though he doesn't have a lot of teeth, you don't need to avoid too many foods. Just make sure what you feed him is soft enough to be gummed.
Good luck
A.