Which oil to use as a top up

[Funky Larma]

We are heading up to white noise at the week end and really want some oil I can top up with jut in case.
Unfortunately I have no idea and halfords is my only option. The helpful chav theta was trying to sell me something with flashing LEDs and a speaker to fit the enterprise.
So I can home and found they do a vintage 20w50 but only in five litre cans, very cool looking cans. But then found a small bottle of extended mineral oil in 10w40. Would this do for an emergency?

No cue the extra virgin olive oil jokes and see what I will end up with :roll:

 

[dubs and classics]

Run of the mill 10/40 will be fine dude

 

[Funky Larma]

Cheers, will pick up a small bottle to keep in the van but once I get the chance I'll change for oil and keep the same brand/grade