What items are farmable in Valheim?
There are only 4 major crops you can currently farm in Valheim, you have already mentioned two.
The other two are Barley and Flax. Both of these can only be grown in the plains biome, however.
There are also other plantable seeds that are not considered crops. Namely the ones that drop from trees (Beech, Pine, and Fir). Oak and Birch trees (the ones you get fine wood from) do not drop seeds currently.