Handy Haversacks are Handy. Other people already iterated on why, I won't repeat them, but they really are worth their 120 pounds-carried in gold.
Although not magical, alchemical items like Thunderstones, Tanglefoot Bags, and Sun Rods can be very useful and fit into a low magic setting. It's not magic - it's science!
Thunderstones are great against spell casters; deaf casters have a chance to screw up verbal spells. You don't need to hit the target either - just the square the target is in.
Tanglefoot bags are just amazing all around. They're useful for escape, taking down flying enemies, making enemies easier to hit... I always keep a few tanglefoot bags (in my Haversack for easy access, of course). They remain useful at high level play as well, because "Even on a successful save, [the target] can move only at half speed." Casters need a DC 15 concentration to cast. Tanglefoot bags are awesome.
Other alchemical items are useful too; they're worth a look. Also, caltrops.
Weapons and armor made of special materials can also be worthwhile. Cold Iron has its uses, as do weapons coated with alchemical silver. Yeah, I know, people point and laugh and tell me that faeries and werewolves are just children's tales, but one of these days... Never hurts to be prepared. Just in case. ...The guards don't know about my 5,000 arrow stash under the floorboards, right?
+Strength bows may also be a good investment. Again, not magical, so it fits the low-magic theme and is still useful. A spyglass may also be a good idea. They're expensive for low level characters, but in a wilderness environment they can be great - and a good non-magical way to spy across a cityscape.