How ambitious are you? That is the first thing that you must consider before you begin to prepare a Japanese campsite.
The most basic thing would be a few banners to give the camp a bit of Japanese flair.
If you don't have the financial wherewithal (or transportation facilities) to have a Japanese tent, at least consider making some jinmaku (camp curtains); they can hide a multitude of sins (among the things they can hide are dome tents, Coleman stoves, ice chests, and nude sunbathing). After banners, jinmaku should be the first things you acquire or make if you are serious about doing a Japanese campsite. If you actually have a Japanese tent, they can even dress up that setting better; there are several different ways of rigging up jinmaku that are recognized, and each one seems to have had a different purpose.
For outdoor events, the next thing to acquire may be bonfire stands. These generally resemble grille-work “buckets” in which a fire is lit, at the top of 3 or 4 foot poles arranged like a tripod (pictured at left). These could be set where ever you desire light; at least two, at either side in front of your campsite, would be the minimum. The only problem with them, of course, is that they are openwork — small bits of burning or smoldering wood might fall from them if you aren’t careful, and you have to be on the alert for fire hazards. Of course, this is a simple thing to prepare for. Ditto the threat of flying embers, which are also problems with bonfires and the like. There are more gaudy standing lanterns, too (pictured at right), which would look very impressive flanking the entrance to a camp.
If you are intending to portray a military camp (which would be great at Pennsic, Lillies, or any of the other longer major “war” events sprouting up), you might want to scatter around a few tate (pavises). These, by the way, also make great tables for spreading out your dinner, battle maps, or someone to give a massage to.
When one considers that there were so few civilian aristocrats out “camping” as to be almost non-existent, it is pretty obvious that a “military camp” would be better. Nobles usually commandeered temples, shrines, and homes of local officials, anyway — which is actually what the military aristocracy usually did, as well. In fact, when akunoya were in the field, they were more likely to have been used as a headquarters rather than a place to stay in, as there was always a nearby temple or house that could be taken over in need.
Other things that would help to dress up the campsite are replacing the ice chest(s) with the Japanese equivalent(s). Of course, this would be merely cosmetic, a thin wooden case to disguise the more plebeian origins of a plastic Igloo container. Real tourney chests in Japanese styles could hold armor, garb, and whatever other gear you may need.
I remember one Pennsic War where someone had brought a portable hot tub; it was made from a huge oil drum cut in half lengthwise, with a wooden lattice in the bottom to keep sensitive buns from frying, and supported by cinder blocks that contained the fire. It was set up inside a separate tent. We got three people in that sucker once. Ah, the War!
There is no end to the dressings you may add. Spear racks can be for holding a pile of spears or a brace of banners. You can have a couple of Japanese style chests to pack the tent, camp curtains, and banners in, which, when empty, can serve to hide your ice chest.
Look at books with pictures of battle scrolls and the like and see what kind of objects were generally to be found at a Japanese camp.
Go crazy. Have fun.