I like lanolin for a final treatment on wood and primary on leather , bone and horn.
Its not acidic and all natural.
The stuff also sticks like poo which makes it good at metal too if you want to make sure to have a complete layer. Oil however sometimes pearls off and I'm never sure if there are any areas where its not.
A good alternative to Lanolin is wax or any other ph-neutral grease.
Renaissance wax leaves a very thin film and is used by museums to preserve leather, metal and all kinds of other things without damaging them.
Grease and wax I only use on blades which are stored for a long time (historical Kukris for example, or Bayonets which I don't really use regularly

)
If I have a knife I use often I just wipe it once in a while with mineral oil. If there ever would be any rust I would notice it soon anyways.
On metal, oil for general use and grease/wax for peace of mind when you don't want to check on rust every month.
edit:
Just a warning regarding leather. Don't experiment too much. In the army I had discovered that liquid floor wax works well on leather boots. The stuff penetrated the leather fast and without much polishing our platoon had the shiniest boots in the whole battalion. Well after a few weeks the leather split into a few layers and the black top layer showed bubbles and became very sensitive to mechanical stress. Basically what seems to work well at first might not be the best solution. Now I am more into prolonging the life of my things instead of going for shininess.