First up, Body Glide. You can buy it at various sporting good stores, but it can be hard to find. Instead of asking the salesperson where to find it and then getting The Look, I now order mine from the Riding Warehouse.
As a side note, I've discovered that the tube keeps getting smaller. When I opened the box containing my most recent order, I was shocked to see that the tube was half the size it was last year. I did some googling and found that the size/price varies from $9.99/1.5 oz. to $5.00/0.35 oz. Riding Warehouse now carries an 0.8 oz tube for $7.95.
Next Up - the Powders.
Another solution, Change Clothes.
And finally, Clean Up and Use Fresh Undies.
Whether you call it swamp ass or monkey butt, sweaty, chafed skin sure is a pain in the butt!