For a larger sized "day" pack (capable of holding a couple of days of clothes and essential hunting gear) I use a North Face Solaris 35 in Olive Drab... North Face doesnt make the pack anymore.. but you can still find them new / unused on ebay, poshmark, etc for very reasonable prices.. I think they originally retailed for just under $200... I saw them last year when I was considering replacing mine for anywhere between $80-$120 for "new"...
I've been carrying mine since 2004... It has literally been hauled all over Iraq, Afghanistan, multiple countries in Africa, multiple countries in Central and South America.. made a few Europe trips with me.. its freaking bomb proof... and also doesnt scream "hunter!" or even "american" when traveling abroad.. I look like any other north american or european traveler/adventurer..
For a smaller sized day pack (hunting essentials only.. spare t-shirt, socks, and shorts are about all you can fit in there with basic hunting gear like binos, spare ammo, range finder, knife, water bottle, snacks, etc..).. I use a Tenzing T1200... unfortunately Tenzing has discontinued this pack as well.. but they have other packs in the 1150-1250 cu inch range..
The Tenzing, like the North Face pack has been exceptional.. its made multiple trips to Africa, Argentina, Peru, etc.. and is my primary hunting pack for pretty much everything in the US as well.. super tough.. very comfortable to wear even when under a full load.. compartmentalized enough that its easy to keep things organized, but large enough compartments that you can actually fit meaningful stuff in the pockets (I hate over compartmented packs)..