Wash the asparagus spears thoroughly under cold water. Trim off the tough ends of the asparagus so they fit into your jars without touching the lids.
Sterlize the mason jars. Wash your glass jars and lids with hot, soapy water. Rinse them well and sterilize by either boiling them in water for 10 minutes or running them through the dishwasher on a hot cycle.
In a medium saucepan, combine the distilled white vinegar, cane sugar, and salt. Heat over medium heat, stirring occasionally, until the sugar and salt dissolve completely. Remove from heat.
Layer the trimmed asparagus spears in each canning jar, add a few sprigs of fresh dill, and chili pepper flakes. (If you are using any of the optional ingredients. Add them to the jars at this time as well.)
Pour the hot brine over the asparagus and other ingredients in the jars, ensuring they are completely submerged.
Place the lids on the jars and seal tightly.
Allow the jars to cool to room temperature before transferring them to the refrigerator. Let the pickled asparagus marinate in the brine for at least 24 hours before serving, but for the best flavor, wait 2-3 days.