Hi!

Chessex is the gold standard for vinyl battlements. I've been using the same megamat for 20 years and it's still going strong. They make many sizes at various price points. Here is a link to their catalog page for battlemats; you'll probably get better / faster service if you buy from a retailer, but they do do direct sales.

Staedtler Lumicolor wet-erase markers are quite nice and durable. Cheap pens tend to die / dry out quickly.

I am also a big fan of these mapping tiles made by an American company called Role4Initiative -- they also make a lot of great game accessories including dice and minis, and these reusable "dungeon dressing" stickers -- these things are crazy cool and useful.

And, speaking of minis, eBay is your friend for mini shopping.

Have fun!