Leave nothing but footprints

It is well understood that we should make offerings to the god/dess and land. There is a good way to do this without pollution. This is not just confined to empty cans , packets and discarded cigarette ends, it also includes empty tea lights , candle holders, 
wax, ribbons and other non bioegreadeable items, Ritual evidence left by previous visitors. 

So what can be offered? small gifts of things which will benefit the animals, birds, and other life such as seeds fruit and gains. Pouring libations into the ground is acceptable. Alcoholic drinks can represent an offering of value, spirits love it. Other natural gifts can include plaits of herbs or even hair tied together. it is the effect that really counts not the size of the offering. If it can be seen from a few  paces away then it's certainly too much.

Keep in mind that if every visitor to a popular site did as you do, there would be a mountain of offerings left to spoil in the place for other users.