Seeking a USB Flash Drive (nearly) flush with MacBook
I'm not aware of any such products with a USB connection, but there are several options for using an SD card slot in this way, if your model of MacBook has such a slot. Some of these are storage devices, while others are microSD card readers, but both types have the same functionality. Note that different models of MacBook have different depths of SD card slot, so make sure you get a product designed to work with your computer.

Here are a few examples:


Transcend JetDrive Lite (64-256 GB)
PNY StorEdge (128-256 GB)
BaseQi microSD adapter
MiniDrive Nifty microSD adapter