Why isn't it socially acceptable for men to carry a bag?  Men have stuff to bring with them too, don't they?

REAL men only carry a wallet and a multitool

Yea we do, it's called a fanny pack but now very uncool to wear.  I used to carry my gun it it, my wallet and other stuff I needed .  It sucks when useful stuff goes out of style

It isn't.  Why do you think it is?

Plenty of guys has a cross body messenger bag. Or get a smaller back pack. 

carry a back pack

It's more socially acceptable nowadays.  Most men seem to carry Back packs/rucksacks/crossbody courier bags and a few braver souls wear over the shoulder or cross body man bags!

When I was serving overseas in Malaysia with the RAAF

We, serving members had what we called a Mum

A canvas bag with a strap that went over the Sholder used to carry Lunch water a Book or Magazine and waterproof 

real men carry Bags and some real men dont carry bags who cares what a man carries

get a briefcase then.

I'm glad I stuck with my attache case when that stupid belly-pack thing came and died.  If you aren't the attache case type, there's no law that sez what you carry in a lunchbox or brown paper bag !!

Men have choices.  Different things can be used in place of a purse.  I used a metal clip board with a storage box attached.