do i need a passaport to travel by land to mexico?

can't say as i don't know what is your nationality!

If you are an American citizen, then ,no. Passports are not yet needed to travel to mexico by land.

You don't need a passport to go into Mexico. Coming back you'll need at least your Drivers License, if your American. Depends how far you go into mexico, if farther than 30 miles, you'll need a visa for the vehicle and yourself, which you can get once you get into to Mexico. Usually their is a checkpoint about 30 miles into Mexico, that's were you get your visas.

I travel internationally every year.

As of Jan 2007, anytime you want to go into another Country, you need a U.S. passport (whatever country you are from). Doesn't matter if you fly there or drive there, you need a passport since a birth certificate isn't good enough anymore. Also, make sure you have a DL on you as well.

No, you don't, but it´s going to be necessary when you return to USA.