This was my first bike packing set up. A mixture of bags from different places/manufacturers: Alpkit tail pack and top tube bag and a Blackburn Outpost bar bag.
The bar bag held my tent, down quilt, inflatable mat, down jacket and a thin fleece sleeping bag liner, all rolled tightly together.
The tail pack held a change of clothes, waterproof jacket, cooker, food, pillow, towel, head torch and a first aid kit. Snacks, tools and a few spares went in the top tube bag.
Having kit, especially tent and sleeping bag/quilt that packs down small is the key to maximising what you can pack.
This is everything (except food) that was in those two main bags:
That set up worked pretty well but I had too much stuff/weight in the bar bag. It was fine on the road and flat off-road but any climbing that was slightly technical/rough meant the high centre of gravity badly affected the steering.
I have gone through several combinations of bags, including panniers over the last 5 years or so and have now settled on a Tailfin Aeropack, 5l fork bags, a top tube bag and a stem bag. This set up works well for me for a 2 – 3 night trip.
(The Tailfin kit is expensive but will hopefully outlast me. Most of it was bought by asking family to chip in for Christmas and birthdays.)