Earth Festival and my lugguage

hello!
currently travelling japan, and im going to the earth festival on the 20-22 of august.
im travelling alone, and i have a B-I-G backpack. im planning to sleep on the beach at Ogi (heard there was some campground).
My question is about my bag. what should i do with it? should i lock it back in niigata and take only what i need? but then it would probably be locked until the morning and im returning to niigata on the 22nd night. is there a place to leave or lock in in sado. please help. im nervous :(
Thank You!

is there a place to leave or lock in in sado.

If you can manage taking your bag on the buses there is a staffed luggage check (free if I recall) provided the Harbor Market area in Ogi Town. Its right at the entrance to the Harbor Market just across the street from the visitor's center.

at im planning to sleep on the beach at Ogi (heard there was some campground).

There's not beach in Ogi, but a bus runs from the visitors center to nearby Sobama Beach campground. I've stayed there twice and it was nice. There's toilets and pay showers available. It costs a few hundred yen for a camp spot, and I'd recommend bringing at least a tarp to put on the ground (available at the conbini), but I'd highly recommend a tent because of the mosquitos. I think they may rent tents as well, but I wouldn't count on that. Make sure you bring some warm clothes just in case. The weather can vary quite a lot. One year when I was there it was ridiculously hot all night, but last year it was freezing cold.

Enjoy they trip, the Earth Celebration is a lot of fun!

Here's some more info:

http://www.japan-guide.com/e/e7677.html
http://www.kodo.or.jp/ec/home/index_en.html