For the benefit of humanity, Pickle and I have undertaken some research and the results are very interesting.
Two ill people can acquire the energy to walk to the shops, buy what they need and walk home by first eating the following:
chocolate brownie, icecream, jelly, chocolate mousse - ideally all together in a bowl, and fast.
However, it is imperative that the larger of the two (who will carry the shopping plus the smaller one at some point) also has a coffee immediately before departure.
Should the two ill people also attempt a meeting with the smaller one's teacher on top of shopping and all that walking, their only hope is that someone gives them a lift home from the last shop.
Unfortunately neither of us are now sufficiently ill to continue our research as planned. We share these results in the hope that others can build on them and one day ill people will not be restricted to sweating in front of screens, eating ever weirder combinations of what is left in the cupboards.