What's the best size camera bag for travel?

For a mirrorless body plus one or two lenses, reviewers across r/photography and packhacker.com generally point to 4–10L slings as the sweet spot for day trips. For a body with multiple lenses, a tripod, and a laptop, 20L backpacks (like the MOSISO or VSGO class) are the consensus pick. Anything larger usually overlaps with carry-on luggage territory.