One good way to extend the decimal system if there are a lot of items to keep track of is to use letters instead of numbers. Since there are 26 letters in the English alphabet, that allows for more combinations.
For example, if people have two digits, there are 26 x 26 = 676 combinations, starting from AA all the way to ZZ. This is compared to 10 x 10 = 100 combinations if people start from 00 and go to 99.
Some examples in the everyday world, such as license places in some locations, use a combination of letters and numbers, which is another possibility to have an extended numbering system.
The googl.gl address for this page is 9Pfw. Which is 22,43652 in decimal.