They are 13 and 12. We don't give an allowance. My daughter frequently has more money than my son. She has a steady babysitting a tutoring gig. He does random yard work for neighbors whenever they need it. She gets money for school lunch, but he brings lunch from home everyday. My son is more involved in school (one sport per season and school clubs) and stays late most days and is younger, so his job options are much more limited than his sister's.
We don't feel the need to keep everything absolutely equal. Our kids are well aware that not everything will always be 100 percent equal between the two of them. They learned that lesson when they were younger and my son doesn't seem to mind that his sister is making more money than he is.