If the work you undertake takes you away a fair distance from your base, then refreshments costs are a reasonable expense that I claim for under motor and travel costs.
I have 6 days a month on rounds/work that are between 10-30 miles away, in these cases its not practicable to return to base to get dinner and if I'stay and collect then I am stuck in these areas till sixish so I have my tea there and claim that as well. As long as you don't' take the p**s than I would consider this a reasonable expense, the worst thing that can happen is that you/accountant have to convince the tax man if he disagrees.