My 'hand bag' must be small enough to fit in my underseat carryon. It should be big enough to hold a small amount of jewelry, passport, reading glasses, a couple of pieces of paper (boarding pass and travel info), wallet and a few meds.

My under the seat carryon has a zip close for the main compartment. A mesh holder for water, a small outside pocket for wipes and tissues and another outside pocket for my 'security socks'. It has a clip for my home keys, a front section for my 'purse', a back pocket for my tablet. The insides are used for snacks (in case of need), my meds and a place to stow my light weight coat for easy access on the plane. My carryon is an old Lands End - I have tried other bags but this oldie is great for me.

I do think it is prudent to keep the valuables in a small bag - which are carried and never set down so you can go to your bigger bag.