When I had the P38 and lived in Ireland, shipping of parts from time of order could take up to a week so I decided to have my own stock of what I considered to be useful parts. Oils etc. are not included as these can be bought anywhere.
From memory, this is what I had :
Full set of gaskets and oil seals for engine (4.6), transmission & axles.
Spare filters (Oil, Air, Fuel & Pollen)
Bonnet release cable assembly
Spare Spark Plugs
Serpentine belt
Pair of propshaft U.J's
Front & Rear Brake Pads
EAS piston & cylinder + spare seal kit, 6mm half hard nylon tube and push in fittings
Fuse box relays, yellow & green
Fuses and various bulbs
Tyre valve cores
3/16" O/D copper brake pipe & fittings
Plus...
A brand new front axle complete with swivels that I bought off Ebay good few years ago at the right price, just in case I had trouble replacing the front swivel ball joints. I managed to do them fine and recently sold it to a forum member.