I had good luck with just a few basic pieces.
A simple coated nylon tarp. Roughly six by eight foot with numerous grommets and/or ties is about right. Rigged flat it is a sun shelter or protection from a light summer shower. Rigged at an angle back to the wind it will hold up to a squall. Rigged three corners down a storm. Strung with all sides tight to the ground with only enough head room to lay under you could ride out a hurricane as long as you set up behind a wind break.
In insect season, about eleven and a half months a year around here, I bring a mosquito net I can rig under the tarp a head net and repellent.
I keep a number of plastic stakes and light lines in a stuff sack. I sometimes have used my walking stick as a pole and have sometimes brought a thin shock-corded pole to help make erecting a shelter easier.
A ground cloth. Two-and-a-half by four foot works well for a lunch break or afternoon nap in good condition. In this size treated cotton canvas is great and will take many years abuse. If you plan on sleeping overnight or the conditions warrant a larger ground cloth is better but to keep weight down you will want to go with a thinner cloth.
If your a bit older, plan on sitting a lot or the ground is less accommodating a small closed-cell foam pad, 12' by 16" works for me, is handy. This can be used to keep that can of beans off your spine, for sitting on cold-wet ground or during food prep or detailed craft work as a convenient flat spot.
A Thermo-Rest, self-inflating sleeping pad, is nice but I have sometimes gotten by with just my small piece of closed cell foam under my hip.
This would be in addition to a sleeping bag, a simple blanket in summer, appropriate to the temperatures. If I expect rain I usually bring an extra garbage bag so I have the option of sleeping with the lower half of the sleeping bag, or blanket, in it safe from the storm. A bivy bag would be the next step up.