One: NotesThe Surface replaces a legal pad in this case. The battery is strong enough to last even a long meeting (>8h). The stylus is precise. Sensitivity was an issue at first, but the configuration app fixed it.
Two: Media TabletMovies, web browsing, reading - I do that mostly in tablet mode using the kickstand to prop it up. If you want better sound, connect a Bluetooth speaker/headphones.
Three: PresentationsPDF works as well as any Windows presentation program. MDP adapters allow to connect to VGA or HDMI. If you forgot your own, just ask another speaker with a Macbook.
You want to control the presentation wireless? The Kensington Presentair is a nice Bluetooth presenter with a Micro USB loading port.
Also, the stylus allows flip chart like presentations.
Four: Mobile WorkIt is light enough to carry around and the display has a high resolution - large enough to use an IDE comfortably. The battery last long enough that I do not carry the power supply. It stays at home or in the hotel room. If I expect to need more time, I take a battery pack with me.
The Logitech T630 mouse does not take much space in the bag, has an Micro USB loading port ans support gestures.
A small UMTS stick provides connectivity at the moment, but I hope for LTE in the Surface Pro 4.
Five: Portable WorkstationWorking in a customers office for some days allows for a larger setup. The USB port on the SP3 is not powerful enough for an external monitor, but the one in the power supply is. I use a MS168B+ connected to a small USB hub with a Micro USB port for power. The hub provides LAN and an SD-Card reader, too. Typically I set it up with the SP3 power supply, but it works with the battery pack. The wireless adapter converts the type cover into an Bluetooth keyboard.
Maybe Microsoft will fix the USB port power issue in the next Surface Pro.