" have zero clothing..." ,...?Oh come now you surely aren riding around buck nekkid ?
But seriously... what ever you are wearing now will serve well enough for anyplace into Mexico and CA.All you really need is a mesh jacket a wind & waterproof shell or liner ( shell is better) , jeans, helmet, some sturdy shoes , a rain suit ,good gloves , fleece pants and a sweater or two . .Make it multi functional, layers that can be added or shed as you go from cool to hot, high altitude to low, items that can work well while off the bike.
In CA you will not encounter the extreme cold of the high Andes and in Mexico stay away from the northern high country and mountains in winter if there is a cold weather system in force .You can alter your route in SA if the temp does threaten to freeze you to death.
Try going slow on the clothing procurement untill you can sample some clothes and opinions and consider what you really need or like. No need to jump right into the deep end and spend a fortune in one swoop on al manner of colour coordinated high tech , limited use bike clothing.