I'll try to help with a little info....
Well, welcome back to the bush, fields, woodlands, rivers and streams.... Your making a good choice to get back into it. You and your son will bond even closer with nature and when your out in it. It can't be duplicated by a single thing I can think of.
Well, let me start with the gun issue... You said he is 13 years old so I will assume he is of average build for a young man. I have a son of the same age so I will tell you what we have and do. We each have 20 gauge shotguns. I have a pump and he has a single shot. I may upgrade him in another year or two. I felt best with his first being a single for the reason to make your first and only shot count. That is how I was taught too. He has a 125.00 New England which is a nice American made product. Check out their website for all the products they make and a few new imports they sell too. My pump shotgun is a Charles Daly 20. It was just over 200.00 and I must admit it is an import. I think it is made in Turkey. It looks and feels just like an 870 from Remington. I like 20's for our turkey hunts in spring, bunny hunts in winter and a grouse or two in the fall. The 20 is a little less bark and bite and to be honest it is all we needed for our hunts. We don't duck or goose hunt. If that is a big part of your plan you might want to think 12 gauge. You will need to decide this on your own.
I would suggest a real good state atlas. DeLorme has just about every state in print. It is the best I have found to date. The atlas shows state, federal lands, parks, hunting areas, land forms, and about a million other very useful points. I think they average around 18-20 bucks. It was the best money you could spend. I plan our trips from start to darn near finish with mine. You can also contact US Dept. of Agriculture-US Forest Service for topo map guide and way to order. These are also great ways to research areas before you ever leave home.
I am unsure if you have been through a hunter safety class with your son? If not sign up and listen and learn. I think it is a great program to go through.
If your not taught any first-aid and buddy care in the class I would suggest you find one and take it too. It never hurt to be up on all we can before we go afield. Due to remote locations we hunt these classes can save lives if the worst should happen.
If your bank account is tight like mine is you can save on some issues that I will list now: Hunting clothes don't need to be much more than a pair of jeans, good boots, and upper garments for the weather your in. I was in the military so most of our camo is my old BDU uniforms and it works just fine. I would think if you went to an army - navy surplus store. A used uniform isn't all too much money. I would think a pair of pants and shirt/coat would be around 40.00. This woodland patern is a good one for my part of country. The brown patern would be good for early spring and late fall hunts in most parts of the midwest.... also at the army-navy you can find hats, gloves, rain gear, footwear, and I suggest a compass. If you have the extra money in your budget you could get a GPS too. I advise if you use a GPS also have a compass. My luck tends to make battery life short and when you need it most -it will fail. Practice with navigation items (maps,gps,compass, and study and know the areas you will be in before going).
As much as I hate cell phones I suggest take it along. I turn mine on only if I need it - otherwise it is off with full charge at the ready. While we are on the topic of safety I should add I carry a butt pack with the minimal smart safety stuff - first aid kit, whistle, flashlights, bic lighter, 20' of strong rope, small camp axe, multi tool -knife, safety blanket (foil type), and a few long life snack type items to have in there for that day when all goes wrong... and it happens trust me...
Well, that is the short list of getting started.... It is just that a start... I would try to buddy up with a local neighbor or friend who hunts and ask for some help and if they would mind to take you and your son out for a day of hunting. Your asking and looking into before jumping full into it is a wise and smart way to get back into a great thing. Let me know how it goes and if I can be of any further help to you....
You know your a good father for spending time with your son. This is the age when a lot of good kids don't have the right direction or leadership from someone close to them. I wish you the best of luck both at home and afield... Rojoe67
PS always pack a camera - I like the little reusable type... The pictures mean more and more as years go by....
ps... And
be sure to have licenses and know all the game laws for what your hunting.... It is our responsibility as parents to make sure our sons and daughters are taught right and wrong in the field too....