PRESERVING WOOD
Linseed Oil: (the boiled kind) rubbed in with a rag or hand is fine in most cases. It's easy and it does some good. There is some objection to its shallow penetration, and some claim that it may raise the grain.
Tung Oil: is better for penetration and it dries hard. Be sure to follow the instructions to avoid stickiness.
Wax: is easy to apply and can be buffed to any degree of luster. The penetration is not as good as oil, however.
French Polish: a commerical mixture of lacquer and other finishes, gives the benefits of both oil and wax, but takes skill to apply.
PRESERVING METAL
A light machine or mineral oil is best, but some prefer wax, french polish, or a rubbing lacquer. The last two are used on brass more than on iron or steel.