There is a widely accepted recommendation that the basic reserve should be about half the precept. That is to cater for inaccuracies in budget forecasting and for unexpected events where the council may wish to act. Or fresh ideas that simply weren't thought of.
Beyond that, it can make sense to have earmarked reserves. Looking at your examples, I'd think office furniture and such like would normally be met out of normal budgets. Unless the closure of the churchyard is imminent, it may be many years in the future, in which case a reserve is not appropriate. I'm not clear how a local council would have a responsibility for highways.
Cemeteries are a special case and difficult to handle. While burials are taking place, they general both income and expense, and many councils do little more than break even, or perhaps just spend any surplus. But a time will come when a cemetery is full, at which point the expenses continue and the income dries up. There is some argument for making large enough charges to build up a fund to cater for at least some of this. On the other hand, options for investment by local councils are limited, and there is an alternative case to be made for simply accepting that costs will rise.
