As important as the models, paints, brushes, glue, flock and reference books. Somewhere to put your brew:
Dig For Victory mug courtesy of the Past Times shop. I think there are a couple other mugs with war-time slogans to look out for too.
Another possible (luxury) upgrade would be a 1940's chocolate biscuit holder, though I'm not sure what one of those would look like? Probably digestives or rich tea biscuits were the austerity order of the day.