I just recently started playing Realm of the Mad God.
You start off with 100 gold, what are the most useful/effective things to buy with it?
You can get a pirate realm key!
And you might be able to dye yourself a few times.
And that, is it.
I'd say don't bother.
Since you get most of the good stuff by looting there is nothing useful you could really buy for 100 gold.
Lately, if you had 100 gold, I would recommend you buy the backpack. It gives you another eight slots to hold items, which is pretty useful.
I used my 100 gold on a xp booster. it was worth it. I probably wouldnt spend it on dye because your probably going to want to use a different character soon or later, because if you do decide to use it on dye you lose your colour anyways when you change characters or die.
What I actually ended up doing is keeping the gold and buying a little more for an alternate character slot. Then I stopped playing totally, but such is life.
Spend it on dyes and keep them in vault, or save for a vault chest/character slot. Take it from someone with 3 years experience :)
I'd say keep it, so you can get more and buy better items.
Realm of the Mad God changed the amount of gold you get when you start to 40. Before, people had abused the free starting gold by making secondary accounts to buy stuff and trade it back to their main accounts. In 2015, the cheapest item (the Soft Drink) cost 20 gold. But you can't buy it for yourself using new accounts because it is soulbound, which means that it cannot be traded to or picked up by another player.