A gym bag is read as readiness and routine, what you carry to keep yourself in shape. A forgotten or lost one may reflect commitments to yourself that are slipping.
Has this come up in your dreams before? What was going on in your life then?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.