The road is now open, but the Tuolumne Meadows store and post office is not. They think the store and post office should be open in early July. My guess is that at least the post office should be open by the time you get there, but there are no guarantees. If the Tuolumne Meadows post office isn’t open yet, they send the packages down to the valley. One option is to mail your package to TM, and then check with the ranger when you pick up your permit. If TM isn’t open yet, you can just pick up your package from the valley before you start your hike. A little more weight, but better than not having it at all.
As for clothing, I generally hike in shorts and t-shirt, but always have powerstretch tops and bottoms (really warm long underwear), either a Polartec 200 or lightweight down jacket, and Marmot precip jacket and pants (great wind protection even if you don’t encounter any storms). I usually also have a fleece hat and powerstretch gloves. You should expect warm weather during the day, but afternoon thundershowers are always possible, and they can bring rain, hail or snow at any time of year. Nights can be cool (freezing or even a bit below) at the higher elevations. I’ve hiked the trail twice – the first time I experienced nothing but sunny weather, the second time I experienced frequent afternoon storms, with rain, hail and even a few flakes of snow. Still a great time though – enjoy your hike!
Kanga