Lot to choose from... too much to consider.
But ... some key stuff.
'Cross-over' to use in many other activities (even though I have way more packs than I should
good back carry - WITHOUT being a constant droopy, butt-slapping bag of cement - sadly, many I see have droopybutt backpacks, especially kids and their school bags...
good sternum and belly straps, help keep the load in place - last thing one wants, in whatever use, is the load sloshing around as you move, especially on bike or on a climb.
I'm not crazy about the mininal attachment points on the current 'skiiny jeans' designed packs - prefer at least 1 web ladder and if possible 2 with each side having a ladder for attaching things adn spanning/carrying stuff.
At least one easy access exterior pocket
Lighter weight pack fabric for small, light loads - bit sturdier for bigger packs. - maybe one internal divider - but not a bunch of fiddly inner stuff....
waterproof is good.

REI Flash 22, circa 2017 model ?

my current go-to for quick and easy is a REI flash 22 (older model with web ladders) - very light weight, simple poly panel for some structure - good sternum and belly straps to keep load on back and not droopy, Single main main, Brain pocket for light, easy access stuff like sunglasses, snack, whatever small thing. mesh side pockets for soft stuff like sunsleeves, etc... 2 web ladders for holding stuff outside (either with Biners or bungee loop) and can easily attach tailight.
Also works as my 'TailBag' on my Moto for 1 or 2 night Moto tours/rides... 22 liters - just about the right size for all day activities or minimal overnight supplies and clothes. Don't like a bunch of hardbags on my Moto, if I can ride without.

Osprey Questa - 27L - circa 2011 ish ?
About the largest Pack I would use - my Osprey Questa - 27 liters BIG! was my daily 'commuting' pack, could carry, work clothes (always ride in riding kit, even winter), light shoes, lunch and sometimes I would carry my laptop from and to work... after 10 years it hardly shows any real use wear. But again - BIG - too big for most riding...
Anything carrying more than 25 Liters I would use a more structured pack with TMP (tensioned mesh panel) structure - the Questa was an exception and a 'test' before I decided to keep and use.

Plain, cheap or expensive Nike/UnderArmor/Adiddas Other basic packs are annoying, slap butt, uncomfortable, and a waste of money when one can get a good designed pack for same price, when on sale or closeout, and is usually well designed for any other outdoor activities or travel.
For super simple - I would use a self-packing (in it's own pocket/bag) backpack - many come from china and some are quite nice - some even have a sternum strap which is key to stabilizing any load.
Ride On
Yuri