1) Your valid Passport
2) Your vehicle log card
One of the simpler way to get to Thailand from Malaysia is thru the Bukit Kayu Hitam located at the end of the Northern tip of the North South Highway.
Total Toll charge from JB custom to Bkt Kayu Hitam (Vehicles with 2 axles and 3 or 4 wheels excluding taxis) is approx RM107.60 and total distance is approx 734km. More info from here http://www.plus.com.my/toll_calculator.asp
Procedure for clearing the Malaysia custom and entering Thailand
1) Present your passport to the MY immigration officer at the counter (just like you're returning to Singapore)
2) Join the Q and prepare your log card
3) Slightly further down the road, you will see Duty free area on the left and a small booth with a MY immigration officer.
4) When approaching the officer, show them your log card
5) When reaching the Thailand custom, if you have pax with you, ask them to alight and Q at any of the counter to get their passport check and stamp
6) You drive further in and somewhere before you enter the custom, check your left, you should see a lane going in and there is a big parking space, just park your car, lock it and bring along your passport and logcard with you.
7) Goto this counter with 'Custom' sign to get the documentation done for your car.
Note: From the pix below, there are 2 different counter at the booth, first get your document done at the counter on the right (somewhere below the 'Form') and when they give you the document, you have to sign the document and give it to the officer in the counter on the left(just below the 'custom' counter)
8) Once you are done with your document for the car, you have to join the Q to get your passport inspect and they may want to take a picture of you at the counter.
9) Once you get your passport done, look over to the exit of the custom and you will see 'Insurance' booth. Get your insurance from there, the rate is base on the number of days you need to stay in Thailand.
10) Once you got your insurance done, go get your car and paste the insurance disc onto your windscreen.
11) Drive it back to the custom and collect the document from one of the officer station outside
12) OK, now you're on your way to your great holiday in Thailand ... Enjoy your trip =)
Note: The above steps are just for your information, providing a general idea what should be done when crossing the border. It should not be used to question the authority if there is any change in the sequence or procedure. I do not vouch and is not responsible for the accuracy, completeness or currency of any information or content provided on or accessible via this site, but however, do feel free to email me if you find any mistake in the above post
Remember: If in doubt, pls ask the officer on duty!!