No pushbutton, just headphone output and slots for SD card & USB flash memory. The memory slots are not in the mockup as the measurements are not in the datasheets nor do I have a board on hand to measure. Depending on the board, I may have to get a larger case. The 9v battery is mounted to the lid of the enclosure with clips and it sits above the MP3 player board. If there is not enough clearance for components, a new box will be chosen.
I am feeling a bit off about having to be tied to headphones for the project - it's a way to further shelter/buffer the user from their environment. An alternative would be just a small box with an LCD display and a vibrating motor so that you essentially receive instructions like a text message or with a pager. The 16x2 character LCDs also offer a nice limitation for text instructions. In this way the user could put the device in their pocket while walking and only have to pay attention to it when it vibrates, indicating that there is a new instruction awaiting.