Do you have some sort of melee weapon as well as your bow? The problem with playing a Ranger early on is the dungeon issue. If you have a dagger or sword available you can hold a torch while whacking away at the enemy.
Unfortunately, Predator Sight potions are fairly rare and are quite expensive. You can buy the Mage's learning scroll in the second town you get to. It is possible that one could turn up as random loot, but I wouldn't bank on it. It is never in the shops in Aridell early on. Pretty much the same thing can be said for Cat's Eye. If you have Mage abilities you might add Gravedigger's Flame which will help your vision in the dungeons. The problem there is that the Flame burns until it is done, and sometimes you don't want to be seen by everyone in the area.
So, either pick up a weapon ability or keep running back to a light source. Challenging little situation, isn't it