Well, one serving of the average US cereal is fortified with 25% RDA (recommended daily allowance sanctioned by the Funny Drug Adminstration for the average Murrikan) of folate. I suspect the folate content is an excuse for banning Vegemite, especially considering that Marmite is still legal.
Let me be very diplomatic and say that you can find decent bread if you are in a major city. If you are out in the boonies, well, the choices can be very limited. In the city, find a good ethnic bakery or go shopping at a place like Trader Joe that carries good bread (and cheese). There you can find European style farmers bread, loaves and sliced, ciabatta, panini, multigrain rolls and loaves, baguettes etc.
Sweet breads aren't really bread. Think of fluffy Hawaiian "bread" (made from sweet yeast dough), and I'd say that's not what I consider bread. Many of the horrid "white breads" (crustless things made from super-bleached flour and packaged in airtight clear body bags) are usually sweet and inedible.
Your partner's cousin may not survive without Vegemite.
Vegemite contains a lot of sodium. When you drink too much alcohol, your body gets dehydrated. I imagine that the high salt content in the Vegemite, coupled with drinking a lot of water after the binge, prevents dehydration and thus alleviates the symptoms of hangover. Not sure what's worse, too much salt or dehydration.