Inspiration - Lauren Conrad
My first instinct to finish a traditionally casual outfit like this plaid shirt and jeans would be to put on some outdoorsy boots and grab a very casual bag. But in the inspiration photo Lauren Conrad made the unexpected additions of sky high YSL Tribute heels and a feminine white Balenciaga bag. I think the ability to mix disparate elements like masculine/feminine, casual/dressy or expensive/inexpensive adds so much interest to what you're wearing and is a big sign of confidence in your personal style.
(Recap from my post here about the knockoff heels I'm wearing: The shoes I bought at Bebe - maybe 7 years ago - and am totally in love with. When I bought them I had no idea they were pretty exact YSL knockoffs. I've worn them to death. The heels are so worn out I sound like a metal peg leg when I walk. I think you can have that repaired? Really wish Bebe would sell them again because every year since I bought these YSL has repeated their Tribute style that almost looks identical and I don't have $800 laying around to buy the originals.)