Everyone has different needs, but there are a few items I strongly recommend you pack when traveling in Saudi Arabia:

• Modest clothes. This one is a given—Saudi is an Islamic country, after all—but men and women alike need to make an effort to stay covered up.
• Travel adapter. Saudi uses the same G-type plugs (3 rectangular holes) that you find in the UK. If you’re coming from Europe or the US, you’ll need a travel adapter for Saudi Arabia. I always travel with several of these adapters since they also have USB outlets.
• Reusable water bottle. Plastic waste is a huge issue in Saudi Arabia, and people love to buy painfully tiny plastic bottles of water. Do your part for the planet—bring your own water bottle. Tap water is generally safe to drink, and water filters are common in metro areas. I love and recommend my Hydroflask insulated water bottle. It also kept water cold when it was boiling hot!
• Reusable cup for coffee/tea/cold drinks. Same environmental logic applies. They’re seriously useful if you’re road tripping across Saudi Arabia—you’ll be drinking a lot of tea and coffee from rest stops along the highways! These travel mugs are great, and insulate both hot and cold drinks.
• Good sunscreen. Saudi sun is fierce, and the dry heat combined with sun can be seriously hard on your skin. Plus you’re going to get some freaky tan lines from all your modest clothing! I always travel with this specific sunscreen because it doesn’t feel slimy or sticky in the slightest.
• Arabic phrasebook. English isn’t very common, especially outside cities. I used Google Translate often… but no one understood me, and it was total crap at translating Saudi’s Arabic dialect. I highly recommend this Arabic phrasebook—it’s specific to one of the major dialects in KSA.