Hi viz yellow motorway jacket. On the web about £29 and only £24 from my local farmers' suppliers, no VAT.
Waterproof, warm, lined, hooded, washable. Only downside is the elasticated cuffs take a long time to dry. I wash mine about once every six weeks; the cuffs take a day and a half to dry properly.
Two side pockets, one top pocket to take a mobile phone, and a hidden pocket inside the flap but outside the zip where you can put credit cards etc. and can access it without having to open the zip and let the weather in.
Potential disadvantage is that the other shooters will think you are the chief marshal.