I have experienced NO problems by carrying on exactly what they allow. All airlines are under a Federal mandate to allow one carryon and one personal item (purse type stuff).
If you go to the website for your airline, they will tell you exactly what they are allowing.
The airlines are allowed to be more strict than the Federal madate but, not more lax.
We flew SWA on Sept. 14th. At that point we had (between three people) one carryon tote (looks like a big purse), one back pack with a digital camera, lenses, smart media and a laptop and required cables and one purse. We encountered a "dusting" at BWI on the backpack, because the batteries for the camera looked like bullets to the xray/scanner machine.
Happy to see that they checked and the "dusting" was painless and fast.
We checked our luggage.
I went to Bentonville AR in mid October, had no problems at all, I carried on a briefcase.
There was a layover in Chicago, I went outside for a cigarette and had NO problems reentering the airport with the briefcase.
The most strident check I had was on the return leaving from the tiny airport in AR. They even made me run my boarding pass through the scanner. Worked for me, they cared.

Just follow the rules and you will be fine.