Yes, many things (like steaks!) are cheaper and better quality. Commisary has Blue Bunny premium ice cream for $2.50 for the new, smaller 1.5L size (no more half gallons). Canned goods are much less, but not all is cheaper, and it's worth it to me, to drive there once a month (they're not open on Mondays (restocking). Gas is usually about 4 cents per liter less; on Buchanan they sell by the gallon, Boriquen (coast guard) sells by the liter. You can shop online; there's the "shopmyexchange" if you have the retired ID card, you can enroll with your SSN, you're "in the system".
You need an ID to get on base, in Buchanan they won't allow "guests" in the Commisary; you'll need the ID to get into any of the stores; Class VI Exchange; (Liquor, Furniture, Outdoor Equipment & Furniture), Exchange, (Sort of like a Super Walmart: Kids toys, clothes, small food and tool section, Lots and lots of huge LED TVs, etc). As far as "special orders"; I wanted a large item, (pro-form HIIT Pro) exercise machine, they special ordered it, and it's been two months so far, but I can't wait to jump on that thing, and do some High Intensity Interval Training. It cost way less than anywhere else, and they've shipped it by slowboat from the warehouse, in US, to (still not) here. You can also buy a car, from the; Military Auto Source. MAS only sell cars that are at least 60% made in U.S., to Active duty, retired, or VA disabled 100%, but a Veteran in one of those categories CAN "sponsor" a civilian to buy a car there. They show you the price, the factory rebates, and Military discounts, and final price. No bickering, no BS, no lies. If being sponsored, you must have your own financing, as they cannot finance you.
If there are any disabled Veterans on here, you can also get assistance with increasing your claim, with many service organizations. I know some folks at the Cabo Rojo American Legion, they've got great records for getting Veterans what they deserve, for their service to this country, (of which PR is a part). PM me, and I can put you in touch with my friend Pancho, he and his wife actually go from Cabo Rojo, to the Mayaguez VA (almost) every Thursday, to help Veterans with disability claims. There's no cost, they do this, as retired, and disabled Veterans, themselves... I'll shut up now