Which element would most likely bond with lithium and form an ionic compound?

Lithium reacts with many non metallic elements; generally it forms ionic compounds. Some examples :-

The halogens, forming halide salts, e.g. Lithium chloride

Oxygen; forming lithium oxide, Li2O; lithium peroxide Li2O2

Sulfur, forming lithium sulfide, Li2S

Nitrogen, forming Li3N

Hydrogen; forming LiH (contains the hydride H- ion)

Carbon;carbide Li2C2, alkyl lithium compounds e.g. LiCH3