The national health insurance system of the Republic of China on Taiwan.
For that matter, the Republic of China on Taiwan. 中華民國萬歲!
I’d choose Adidas. I already buy their products even though they charge way more than their competitors, so a lifetime supply would certainly be convenient.
Polar seltzer water. I’m always saying, natural flavoring, no sodium, and it’s carbonated!
Wasmund’s Single Malt.
LemiShine. We’ve got super hard water and no water softener. (Yet. We’ll get one eventually, but have other stuff to save up for first.)
LemiShine’s amazing - it’s restored my husband’s favorite plastic cups. It’s gotten off all the crud that was starting to build up on the glasses. It makes my dishes shiny and sparkly. I was beginning to despair, even after replacing the dishwasher with a new one (oh it needed it, how it needed it, but still). It’s a wonder product. I love me my LemiShine.
I think I would have to shill for Dollarama. You can get all kinds of things there and it’s all just a buck or two. I got everything for my son’s birthday party (craft supplies, plates, napkins, loot bag contents) for under 50 bucks.
The first thing I thought of when reading the OP was my 98 Honda Civic, which I’ve praised several times in other threads on this board. Probably one of the most reliable cars made in the 90s. I would definitely endorse Honda (although I’ve heard that later model Civics aren’t as good–any truth to that?)
I also like Amy’s (and I’m also a vegetarian.) My favorite is the pot pies.
First instinct - Apple, specifically my much loved and abused iPad.
If was motivated by what I could get but still within the scope of the OP - WestJet. Reliably better service than any other airline I’ve used.
Dremel tools.
Newegg. Great prices, great service. And a lifetime supply of computer parts and gadgets would make me one happy FlyBy. (I worked for a custom computer builder for a while. Newegg averaged maybe $5 more per item than our wholesalers did, and had far better service.)
If it has to be an actual product and we’re getting paid in money, I’d probably choose Maglite flashlights. They are the best designed, most functional, and highest quality items I know of - and they’re beautiful as a result. That is what all manufacturers should aspire to.
Tough to say, I’d have to look at the money aspect. I’d think of a product that I would get free, but could resell for a lot. Say I sponsor Boeing and get a free jet. I’d use it a bunch and then sell it for a few million. 
If that’s too over the top, maybe the less pricey automobile market. I would be OK with a new Ford or Chevy every couple years. If I had to trade it in each time instead of selling it though, I’d pass.
If the plane or the car are not acceptable, I’d probably go with some technology brand or computer company like HP (they haven’t backed out of making PCs again have they?). I could build myself a nice rig whenever I needed one.
My first choice would be the elephant hospital in Lampang province, northern Thailand.
But I’m not sure that can be classified as a “product.” If going by the strict definition, it would be Singha beer.