VE Day is being celebrated on 8 May 2020 and it’s classed as a Bank Holiday ( yep in Scotland as well) so no post on the 8th. It will be tight you should get it if you post first class on Tuesday but wheels could come off.
I am sure somebody will be along shortly to give local advice. 😎

Thanks Byron

I will omit that re- supply drop and just start with 2 days extra food.
William:flag-bb:

If your parcel is under 2kg why not send it "Signed For" or "Special Delivery" that way you'll know when it's arrived and give you peace of mind. Special delivery is usually guaranteed for 1pm the next day ex bank holidays etc.