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Go for something small like the big top or one of the bigger saddle bags from wiggle/chain reaction. As Scott said large saddle bags are rubbish unless their packed full and with a bit of consideration.
Things like shoes are likely to cause headaches when packing, I'd be tempted to lash them to the outside of the bag with a ski strap or similar.
Bike packing saddlebags aren't a volume you can just chuck stuff in, close the lid and ride off like you'd be able to do with a Carradice or box shaped rando bag.
I am seeking a bag that'll take a rain jacket, body warmer and possibly tools and some flip flops or barefoot shoes.
Bar bags all seem to interfere with garmin and lights - my k edge mount has Garmin out front with light underneath.