Need recommendations for a simple top-loading backpack (roll-top, envelope or brain) that's comfortable to ride in. Preferably made in USA with few doodads.

What's wrong with backpacks that zip all the way around?

Grundens makes a dry bag backpack, as does seattle sports, Ortlieb ,
cascade designs, etc.
look in the water sports stuff, a Portage pack is one you wear
to walk with your canoe over your head from one body of water to the other ..

Shoulder thwart on canoes is at the balance point on them ..

Made in the USA= Expen$ive, so how much you willing to spend? On the cheap would be Banjo Brothers imported stuff, then it just goes up from there- Chrome, Mission Workshop, Seagull... countless others out there.

Most people inquire about the comfort level while riding "with it on" or "wearing it", but I think this may be the first one wanting to know while inside it...

LL Bean has a rucksack that opens at the top. There is also a pocket on each side and a zippered pouch as well. I've had mine for more than 15 years and it's fairly comfortable to ride with it as long as I don't go nuts and shove too many groceries in it.

I have a banjo brothers bag that I like a lot. Not USA made but durable. It's one big top loading pocket with a flap that clips over which can be used to strap on larger cargo.

Yeah, I've had the large, original black version since the fall of 2009. Like the bag, it's just that it's bigger than I thought it would be- or maybe the design allows for it to be overstuffed and still secure the flap.

Mission Workshop Sanction Rucksack. Waterproof. Sturdy. Simple. Made in the USA with lifetime warranty.

Timbuk2 makes some. I have this one...
https://www.timbuk2.com/tb2/products/...ckpack/2114822

It holds a good amount of stuff and is pretty comfortable. I do plan on making some modifications this year though. I am going to add a waist strap for when I have really heavy loads and also a compression strap around the top. The top squared-off corners make it harder to see behind you while riding, so the compression strap will pull those corners in and out of the way.

I just bought the Timbuktu2 Track II backpack. Yeah, I know it's got zipper closures. It's got everything you need, nothing you don't. I like it because it's simple, yet holds a lot and keeps things organized. I especially like the outer front pocket that holds your helmet or anything oversized.

Osprey Flap Jack

I've been riding with a Timbuk2 Hemlock - Medium, for about a year now. It swallows anything and everything I can throw at it. It's from a U.S. company, but not made in the U.S. Really simple design, two cargo compartments (one large cavern, one organization/smaller item pocket up front), one laptop compartment. I was worried about the narrow straps and no chest stabilizer, but honestly, it's one of the most comfortable backpacks I've worn and I use it for everything. It's also not too expensive (~$100). If you want a quality, made in the U.S., rolltop that can hold a bunch of stuff, my choice would be the Mission Workshop Vandal ($279). Pricey, but that's what I'm going for next.

+1 Mission Workshop.

https://missionworkshop.com/

Look at Duluth Pack; nice quality, durable, made in the USA, comfortable.

Duluth Pack make very nice bags.

Banjo Brothers large commuter backpack is what I've been riding with for a couple of years. Very durable and large. Even has a replaceable waterproof liner on the inside to keep your stuff extra dry.

That is an understatement. If would've been able to see the L next to the M in person, I'd have opted for the M. I wouldn't suggest the L unless you're planning on hauling a guitar or potted tree or something.

+1 MissionWorkshop

I like my Banjo bros, but... the outside pocket flap ripped after one season.

Really simple? a rectangular bag with a grommet in the bottom corners
the drawstring at the top, long enough to tie in each grommet, when the bag is opened.

when the draw cords pulled to close the top, they become long enough, to become shoulder straps.