What's the most effective way to prevent foot and back pain at work (cashier)?

Standing pain: Soft mat, good athletic shoes and proper posture would help. Change position or stretch every 10 min. Or so. Check for any other symptoms such as pain radiation down the leg, tingling or numbness in legs etc. If pain increases with leaning forward it could be a damaged disc, if leaning back increases the pain, it is the lumbar spinal joints. Muscles get sore after tending for long time.