I have used this for years: Herschel Raven. If all you have is a few cards and some cash, it’s awesome. If you don’t carry cash, you can clip it onto your pocket to secure.
Popular alternatives to
Herschel unisex adult Raven...
AZMED Maternity Belly Band for Pregnant Women | Pregnancy Belly Support Band for Abdomen, Pelvic, Waist, & Back Pain | Adjustable Maternity Belt | For All Stages of Pregnancy & Postpartum (Beige)