The best autumn fishing happens in weather most people would rather avoid, which means the difference between a good session and going home early is almost always clothing rather than tackle. I have spent forty years working out what matters and most of it is simpler than the marketing suggests.
Three layers, and each one has a job
The base layer moves moisture off your skin. That is its only job. It must not be cotton, because cotton holds sweat and then chills you badly the moment you stop moving. Merino or a synthetic base layer, close fitting.
The mid layer traps air. Fleece or a light insulated jacket. This is the layer you add and remove during the day as you warm up walking and cool down sitting.
The outer layer stops wind and water getting in while letting moisture out. This is where the money goes and where it is worth going.
Where people go wrong is wearing one very thick thing instead of three thinner ones. You cannot adjust a single thick coat, and you will end up either sweating or freezing.
Waterproofs: taped seams and a decent hood
Two things separate a waterproof that works from one that does not, and neither is the fabric name on the label.
Taped seams. If the seams are not taped, water comes through them regardless of how good the fabric is. Check before you buy.
A proper hood that adjusts and moves with your head. A hood you cannot see out of when you turn to look at a rod is worse than no hood, because you end up leaving it down.
Beyond that, look at whether the pockets are usable while you are sat down, and whether the cuffs seal. Wet forearms from water running down your sleeves is a specific misery of autumn fishing.
The wader question
Chest waders or thigh waders is the decision people get wrong most often.
Chest waders are the sensible default for river fishing in autumn. Higher water means the wading you did comfortably in July is now deeper, and a wave over the top of thigh waders is the end of your day. They also work as a windproof layer even if you are not wading, which is genuinely useful on an exposed bank.
Neoprene is warm but sweaty and hard to walk in. Breathable waders with a separate insulating layer underneath are more versatile and far better if you are covering ground.
Boot soles and safety
Felt soles grip wet rock far better than rubber. The complication is biosecurity, because felt holds water and can transfer invasive species and disease between waters, and some fisheries ban felt outright. Studded rubber is the compromise most people land on.
Whatever you choose, use a wading staff in autumn. Higher, coloured water hides what is underfoot and the consequences of a slip in a cold river are serious. Wading belt fastened, every time, no exceptions.
Hands, head and feet
You lose most of your comfort at the extremities and they are the cheapest to fix.
Fingerless gloves or fold-back mitts so you can still tie a knot. A hat, because a bare head in a cold wind will beat any jacket you own. And proper socks, wool rather than cotton, with a spare pair in the bag.
A small towel to dry your hands is the least glamorous and most useful thing I carry from September onwards.
The things people forget
A flask. Not a luxury, it genuinely extends how long you can fish comfortably in the cold.
A spare complete set of clothes in the car. If you go in, or if it buckets down for four hours, having dry clothes to change into is the difference between an inconvenience and a miserable drive home.
And a seat that keeps you off the ground. Sitting on cold wet earth drains heat out of you faster than anything the weather can do.
What I would buy first
If the budget is limited, spend it in this order: a genuinely waterproof jacket with taped seams, then good socks and a hat, then a mid layer, then waders. Most people do it in exactly the opposite order and wonder why they are cold.

Mike Talbot grew up in Cornwall and had a rod in his hand before he was tall enough to reach the rod rest properly. His early fishing was mackerel from the harbour wall and plaice on the beaches at low tide, but bass took over in his late teens and have never really let go.
He moved to Pembrokeshire in his thirties for the coastline as much as anything else, and now fishes a mix of rock marks, estuaries, and boat trips across West Wales and the Bristol Channel. He targets bass on surface lures through summer, drops down to soft plastics and HMDs through autumn, and fills the winter with wrasse fishing on the rock marks when conditions allow. Personal best bass: 8lb 4oz, caught on a floating stickbait at first light on a calm August morning.
At The River Bend, Mike writes the sea fish species guides, sea fishing technique articles, and the coastal access and regulation content.
Covers: Bass, wrasse, mackerel, sea bream, pollock, sea fishing techniques, shore fishing, boat fishing, tidal and coastal access rules