surface pro 3
What accessories do I need to purchase with a surface pro 3 and do I need to buy a different adapter than the one that comes with the surface pro 3?
I don't recall an adapter coming with my SP3 so I'm not sure what you're referring to. It came with the power adapter to recharge it, if that's what you mean.
As far as adapters in general, you may need one of the variety of adapters available to use with the SP3's mini Display Port to go out to an external monitor. Depending on the type of monitor connection (VGA, DVI, HDMI etc.) you can get the one you need from places like Best Buy or online.
As far as accessories, I would highly recommend the Type Cover. It completes the SP3 and is a very good keyboard while offering protection to the screen. If you want to backup your data locally you might want to consider a USB 3 external drive. If you have a number of peripherals you use you might want to consider a USB 3 hub or, even better, a MS Dock for the SP3. Best Buy handles a Platinum padded sleeve made specifically for the SP3 that I would recommend. It looks very nice and has an additional zippered pocket to place your charging cable, USB sticks etc.