I've just given into temptation and purchased a Ghillie kettle so we can boil water and make tea or coffee while we are working on the orchard at Turnditch. These don't need gas or electricity, just a few dry twigs to quickly boil some water in any weather conditions.
So now we'll be able to provide hot drinks for visitors and volunteers on the orchard. I guess I'll have to get a stock of camping mugs to hold on the site.
Edit (15 Oct 16)
I now have a stock of mugs, tea bags, biscuits etc., but they won't be held on site. We'll bring them when we're working on site.
I gave the kettle a test yesterday morning and it performs really well even in the rain.