I have some apps on my phone that can come in handy. Some of them are a clinometer, unit converter, sound meter and a graphing calculator. I used to have a mechanical engineer app as well, that would calculate so many things for you involving pipe sizes, thread sizes, gears, etc. Smartphones are an engineer's best tool that's on you all the time. If you're dealing with material specs a lot, matweb is a pretty useful resource for deciding on a material.