Reddit reviews GMAT Official Guide 2018: Book + Online

To get an idea of the resources you'll need, I suggest that you take an official practice test. It may be the case that you're already scoring above your target score, in which case you may not need to prepare at all :-).

Resources-wise, be sure to get GMAC's Official Guide for the GMAT, which you already have.

For extra practice questions, the test maker has a quant-only book and a verbal-only book, each with 300 questions.

As far as instructional resources go, the one that's best for you will be the one that best suits your learning style.

In addition to learning the core concepts and GMAT-specific strategies, be sure to work on your endurance and test-taking skills (e.g., time management) by taking several practice tests.

Cheers,
Brent

I bought something like this on Amazon, and there was a code inside the front cover.

Amazon OG 2018

Eh it's OK. It just allows you to complete the OG problems online, which could be helpful to get used to doing problems from a computer screen.

The biggest drawback is that you can only have like 25 saved sets (which adds the questions back into the pool). So for example, I like to do problems in sets of 5 or 10 and then review. Once you've completed the set, the results are saved and the questions are removed from the pool of questions. Once you get to 25 saved sets, you have to delete a saved set to do any additional problems. Really annoying.

If not for this drawback- I would be a big fan. That said, it can still be helpful I think.

For screenshots- click the link and scroll down to reviews. There are a few customer images which show the interface.
https://www.amazon.com/GMAT-Official-Guide-2018-Online/dp/1119387477/