I recently did an overnight trip in this hot, muggy weather we are having; we had the same temperatures you mention. About all I used was my tarp, quilt, stove, and rain gear. The first day we walked about 10 miles and all I wanted was to stay cooler. Shorts and a light synth with trail runners and light wool socks were all I wanted. I slept under a tarp with a 30 degree quilt only. The quilt was overkill but I could vent and be comfortable; just a little of it over me was plenty. We had a fire at night mostly to keep the bugs away and I needed nothing else.
The second day rained hard most of out 7 mile trip out. I had driducks over a synth T and was fine. Some of my group had no rain jacket at all and were fine too.
The next day I was covered with chiggers from about mid-thigh down. Of course I never saw or felt them while we were out but they hit with a vengeance the next day. While the trip was enjoyable, I really don't think I will backpack again at low elevations in August again.
I would think about experimenting with a light alcohol stove too. You really save a lot of weight on short trips like these. Get a cat food can, a hole punch, a bottle of HEET and a little tin foil and you are ready to give it a try.
If you know the area and trails are well marked, I see no reason for compass, rescue devices, backup anything, etc.