When standing still, have one foot higher than the other, it really works, like even a level of a 3" to 5" can make a difference when standing idle. If working on concrete, get soft soled shoes, like cushions. Trying exercises like walking on toes for a minute. Sitting down on a chair, bring your legs up and stretch your foot all the way forward and then all the way back (may have to have someone help you with this one), it stretches the tendons and muscles you have used one way all day.
Taking baths with epson salts helps (clear with GP). Make sure (via blood work) you have the right balance with potassium, magnesium, and calcium, to keep the leg pain away. Also stand two feet from wall, hold the wall and lean into the wall by relaxing arms, helps with legs. Also massage legs from foot to knee. Keep hydrated.
When you can get a break, put feet up, if you can, higher than heart, helps with the blood circulation. If your feet swell, make sure you have good shoes, see GP to make sure you don't have an underlying medical condition. Compression stockings for men and women are available to help keep the fluids from staying in legs and feet (see GP for guidance).
Back pain requires actually exercise and make sure there is nothing wrong first medically. Lot of stress from standing all day. Swimming is good as a relief, so is yoga and massage. Generally, people that eat right don't need supplements, but who eats right? Balance your meals with lots of greens, fresh veggies, light on meats and beer. Too much calcium like dairy can cause a buildup in blood, so balance is important. Try to stay away from corn products, seems there are people that are on their feet all the time, getting off of corn does help, but they don't know why yet.
Sometimes my son, after being on his feet all day says he feels like he was hit by a truck, God forbid, but he goes on his bike and weird, using different muscles helps the ones he overworked, so try it. If you have no medical problem, sometimes a hobby like bowling can make the difference because of the way we move or not move all day needs all the muscles working.
When tired, do put feet up, massage legs and feet, use pillows for back support and chill out.