They do this by offering emergency relief funds for natural disasters, interstate highways for trade and economy, and all manner of things.
I think a federal minimum wage makes sense in this system, ensuring that the people of Tishomingo, Mississippi have the same fundamental buying power as the people to Los Angeles, California instead of them earning $1 an hour because it's comparatively cheaper to live in Tishomingo.
Raising the federal minimum wage is also a good way to decrease old debt, deflate the value of stagnant money (increasing the likelihood that the money moves, improving the economy) and to temporarily boost the financial status of the poorest and most disaffected.
In an age where no one working minimum wage can afford the cheapest 1 bedroom apartment without an extraordinary stroke of luck or some sort of financial dispensation, someone needs to do something and it needs to come from on high.
That being said, if you are pulled over by a federal agent in a legal state, if you meet the federal requirements you can still be prosecuted for possession of marijuana at the felony level, that being said, unless you were doing something super sketchy like having a full pound of weed split into little baggies or something, that is unlikely to stick.