When making or purchasing your favorite rub usually the most economical way is to do it in bulk. This is especially true when ordering ingredients or ready made products through mail order. Shipping these days is through the roof. There are some rubs I purchase in five pound packages and over time, even in the California Central Valley humidity can cause your rubs to clump.
One day while fighting with a particular clumped up bottle of rub I remembered an old trick I saw once in a little diner. They had placed saltines in their sugar and salt shakers to keep them from clumping. It works with your rubs too!
Place a saltine or two in your big bottles of rubs and they will be much less likely to clump. Over time you might need to change out the saltine, but it’s a rather easy process. If you’ve got the smaller rub bottles use those little “oyster” crackers. They’ll fit in the bottle and not interfere to much with your shaker top.
Saltines will work well with most rubs but if you’re using a rub that is high in brown sugar toss in a slice of bread instead of the saltine and it will help to keep the humidity from turning your rub to concrete.