Bags are meant for using.
Beach - V&A McQueen bag or one of those free cotton shopping bags you get from fashion or art shows
Park / outdoor day out / outdoor concerts - one of my coated canvas
Gucci Bostons, Cambridge satchel, 1969 patent Gucci (partly ruined anyway from being 'babied' too much and kept for best, it prefers what no other bag likes, lots of action and rain). Liberty Boston, Hermes Garden party or Chanel Cambon shopper.
Gym / dance class / martial arts - Paperchase holdall or Burberry backpack
Rainy day - light or intermittent normal (vertical) rain, Bal Holiday Bowler or Cambridge satchel both shiny coated leather rain runs off. My liberty briefcase.
Possible rain but want to look nice, BV Cervo hobo or other bag that doesn't seem too mind the rain too much but I'll fold and carry a large plastic carrier and carry an umbrella. Possibly small crossover under a coat.
Heavy, heavy rain (horizontal) and full force 10 winds - parker with inside pockets, arm pockets and plastic poncho, over trousers waterproof hike boots.