Well, one leaps to mind: The therapeutic Waterbed. Heinlein described it in detail enough that there was some issue on the patent.
Stranger contains an early description of the waterbed, an invention which made its real-world debut a few years later in 1968. Charles Hall, who brought a waterbed design to the United States Patent Office, was refused a patent on the grounds that Heinlein's descriptions in Stranger and another novel, Double Star, constituted prior art.
This site lists 119 inventions credited to RAH; I'm not sure I agree with them all, but it's interesting to look at. I think it is more of a 'Credit for the Idea' than a true list of inventions.
Also he didn't invent them, but he's the source of the term 'Waldo' for remote telefactoring devices.
Too many to list here. A few are:
- CAD/CAM software, from A Door into Summer.
- Robotic Prosthetics, from Citizen of the Galaxy
- Computer Controlled Cruise Missle, from Citizen of the Galaxy
- Genetic engineering, from Between Planets
- Waldoes (remote manipulators), from Waldo and Magic Inc
- Computer controlled showers, from Starman Jones
- Voice activated security locks, from Stranger in A Strange Land,
He used the concept of portable phones in many of is novels starting in 1948. The basic concept of his "pocket phone" was just that, a phone that fits in your pocket and allows you to make phones calls from anywhere.
He came up with an idea strikingly similar to velcro in 1957's The Door Into Summer. Velcro was patented in 1955 and the company built an office in the US in 1957, with the US patent filed in May of 1958.
He also predicts the internet in a couple of his books. His first attempt was not digital, but pneumatic, and involved live librarians who sent you copies of requested data.
His second attempt, which was in 1983 was a bit more on point, but since the internet already existed, this isn't as amazing, but what is pretty cool is how he describes using the technology and getting lost in endless clicks while doing research.