Hard question to answer and each visitor must decide for themselves but at the summer solstice this year i was at the WKLB, anything other than simple organic offerings i binned.
Leaving food in that particular barrow i feel is stupid too, lots of people sit in there during visits and a puddle of rat piss isn't really gonna help you health wise is it.
I blew out all the tealights and candles that were burning against stones and gave them to some travellers i met at the ridgeway.
Hate me for it if you wish, i don't really care, preserving the stones is what really matters to me.