You can take such handy Craft skills as Craft(knapping), Craft(woodworking) etc, if you like. Craft(bowyer) is a separate skill for making bows (from any material) but woodworking will suffice for arrows. Or Craft(bonecarving).
On second thought, yes to Craft(prim weapons), which covers weapon-only uses of knap, woodwork and bonecarve, but not bowmaking. Makes sense, since Craft(weaponry) applies to metal-forged weapons. Craft(armourer) applies to metal armour (you probably don't have this unless you were from the settled lands), but you'll want Craft(leatherworking) for leather and hide. Further tip: If your plan is to use leather rather than hide armour, Craft(tanning) is your friend, though you can do that untrained.
To borrow from the Civ tech tree, the following techs are known to be available to you in the plains.
Fishing, the Wheel (but usually only applied to), Pottery, Animal Husbandry but not Agriculture*, Horseback Riding, Hunting/Spears/Javelins, Simple Archery**, Mysticism***, and Mining.
*Theoretically it's known, but your people aren't sedentary enough for this.
** Fairly rare. Throwing spears are more common.
*** Druidic animism is the favoured 'religion' in the plains. Gods are more favoured in the settled lands.
Edit: If you get a bow, you may start with ten arrows. If you choose a javelin, you start with three.