Balbert, I have quite a bit of finishing experience and I would suggest the following things:
You can do many things and it all depends on how much effort you consider worth it, being it is a storage unit in the attic… not to mention how well or with what you are equiped to do the job, as in do you have a spray gun? or are you doing this with brushes?
For the natural version; non toxic (you mentioned liking less chemicals and more natural) use Schellack. Its non toxic, (except the alcohol that you use to thin it) and its relatively easy to apply with a spray gun, but also can be used with a brush. From personal experience, with the spray gun its a dream, and makes the "wet look" while showing off some grain and figure from the wood, and if its a Attic storage unit, you will it will not be necessary, more than likely, to have to polish it to a super high gloss, as long as you can spray it evenly without runs.
Not so natural is of course Polyeurethane, (Lack as I call it because its shorter), is quick easy to use no matter if water based or not. Lack you can buy also in highgloss and is only a matter of sanding to 150 to 180 and spraying/applying with brush, let dry and sanding again with 240 then spray again… nice and easy and quick, can be done in one day with use of proper lack.
The water based Lack is actually harder and more durable but more dangerous to spray because the particles when spraying are water based and can bond to the soft tissue (also waterbased) in your respitory system and you need just to make sure you have a mask when spraying and using.
Oil the other major finishing product is also good and easy to use, although a bit more drying time is required and a bit more time need (in my opinion to get a non sticky clean surface), because of all the excess that needs to be wiped away to alow to "dry" (actually oil polymerizes, a reacation with oxygen, heat and the organic makeup of the oil).
As for oils, I do not know what products (brand names you have there in the States), but I would suggest using any sort of oil that will harden out within 24 hours (two types of oils are those that harden and those that do not, underneath that there are oils with chemical dryers in them and those that do not, those that do not have any sort of drying accelerant in them, take sometimes 7 to 10 days to harden out and are good quality, and all natural, but take for ever and in my opinion as someone who works in time pressure and where speed is everything, are not worth it.
so you can also get oils that are mixed with hard wax and the oil soaks in and hardens and the wax stays on the surface of the wood and forms a sort of film, which can be buffed out to a "semi gloss" at most. Its a bit like putting shoe polish (which is wax mostly) and polishing the shoe. My favorite method is to use a normal hardening oil first, let it dry, then sand, then applying a Hardwax-oil as the final coat, very thinly, and before it drys and gets too hard polish the semi dry wax (it will start to get really tacky to the touch) with an old soft t-shirt (or rags made from one) and let it dry overnight again and you have a "slightly wet/glossy" look and the grain and color pops out because of the oil undercoat. For oil the perhaps "disadvantage" would be you have to sand to 240 (in my opinion anyway the results are better to the eye and the touch) then first oil application, then sand again (240 again or perhaps 320) then oil again, very lightly.
I tried to keep this short but, finishing is a complicated and manifold subject, with many finishing options.
Hope i could help and did not bore anyone do death!