If you stay shallow, use a small tank, and have a long surface interval, you don’t need much at all. As they said back when: “you can’t get bent on a 72”. No need for depth gauge if you know you’re staying shallow. No need for timer if your tank is too small to stay down long. No need for tables if you don’t track your depth and time. No need for SPG if you use a J valve. (Okay, maybe not that last…) If the very limitations of the situation prevent you from even being able to reach dangerous levels of saturation, why carry a gadget to keep track of it? For that matter, why buy an expensive wetsuit when you can glue one together yourself with a pattern in a magazine?!
That old-school sleek minimal look has a lot going for it as long as you stay on the very “rec” end of the rec-tech spectrum. You should probably buy a computer anyway though because pushing things further is a lot of fun.