Most small-to-medium DSLRs (e.g. Canon 5D, Nikon D750 without a battery grip etc) with a small-to-medium lens attached. Plus 1 or 2 lenses spare or a speedlight.
Almost any mirrorless/CSC camera (e.g. Fujifilm XT-4, Sony A7IV, Canon R6, Nikon Z7) with small to medium lens attached. Plus 1-2 lenses spare or a flash.
Two rangefinder cameras (e.g. Leica M10 & Leica M6) with almost any lens attached.
Almost any bridge camera (e.g. Leica V-Lux 5, Sony RX10 IV, Lumix FZ2000 etc) plus space to spare.
Medium-Large binoculars (e.g. Canon 10X42L IS WP or Nikon EDG 10x42) with space to spare.
Small foldable drones such as Mavic Air 2 or Mavic Mini 2.