Essential equipment to bring to MX?

One thing we used almost daily is a 5 gallon bottled water pump. It operates on D-cell batteries. It sure beats trying to lift the bottle. Got ours at Walmart in Nogales,Az. It is also available online

I would not worry about any drive train parts, if something is not available locally the part is only a day or so away.
The parts that are exclusive to an RV are harder to come by, although DHL will deliver to your door but the price is high.
I would recommend a water pump for the RV system, low water pressure is the norm and as a result your on board pump does get a lot of use. A spare sewer hose is a great idea since sometimes the hook up is a bit farther away than in other areas of the world.
RV's sometimes use special light bulbs in the interior, if yours are the normal type bulb it is not a problem but if it is something exclusive to RV's, bring a few spares. You can always order more as time goes by.
It seems to me that over the years the control circuit boards for the refrigerator are by design very fragile and prone to failure. To me, after reading about and seeing numerous failures over the years, it is just a poor design and a real moneymaker for the dealers. A surge protector may help but I feel selling a $12.00 circuit board for $200 is why they act like they do.

I carry a spare water pump and have had to replace one in Mexico. Water pressure is almost always low so we use our pump most of the time. Fans since you may not be able to use AC when needed due to low power. Many of the parts mentioned already. Tools. Never found anyone to talk to on a CB.

Thanks everyone!
My RV has 22.5" wheels, I heard tires for these are hard to come by in MX?

I asked that question on a diesel site forum.
They suggested stuff like hose clamps, spare hoses, fan belt, fuel filter and extra fuses for the engine.

I'm going with the mexicorvbuddies.com group

Take a surge suppressor. At least for us - electricity can be tricky in MX. Read the Church's book on that - they've got some great suggestions.
We have not found many parts for an RV - so anything you think you might need that are unique to your RV are good. We now carry extra fuses (since electricity can be tricky - we've often blown fuses and needed replacements).

Good luck and have fun.

Spares of anything that You can manage to find room for. That said it should be stuff that You are capable of replacing Yourself.
There are some Tire Sizes that are hard or impossible to obtain in Mexico, not just RV Tires , so be aware and carry spares in all Your Tire sizes.
There are very few sources for RV related parts , things like Sewer Hoses ,Black,Grey gate valves are not readily available even in larger Stores like Walmart in Mexico.
There are No Hawkins Cheezies anywhere ....Only available in Canada eh!

From the big cities down to the medium towns you will usually find at least a Wal-Mart or Sonora with almost anything you could buy in the U.S. Of course there are some regional things you might want to take. Like I take Tillamook Cheese products, Decaf Lipton Iced Tea Bags, Chinet oval paper plates and Oberta Dry Salami. But by now they may even have those now. I know that sweet pickle relish used to be impossible to find, now even the smaller Mini-Supers have them.

But primarily I go a little native and eat Mexican, that's one of the main reasons I'm down there. Believe it or not, I seem to do better with my Diabetes in Mexico than I do in the US (as long as I don't pig-out on the Chocolate Flan).