He he, a little confusion here
Kicky:
Ho voglia di prendere un Pepsi. correct (except the fact that "pepsi" is a female, of course, because should be a brief form pepsi-cola), but a little formal, however "ho voglia di bere una pepsi" well, you could tell this even to your best friend or to your girlfriend, the formal tone meaning you seriously want a pepsi.... well, actually one girlfriend of mine surprised me quite, once: we was in the middle of a birthday party, and she told me in one hear "Ho voglia di fare l'amore con te".... an offer nobody could resist....
Mi sento di prendere un Pepsi. uncorrect: the meaning is different. "Mi sento di" means I feel I'm capable to... When you ask that to someone you say that you doubt he will, so "Te la senti di mangiare un gelato?" Could be an offer after a big dinner: the answer "No, thanks" would not surprise you. It could be also a friendly form of challenge, like "Te la senti di fare una corsa?"
Ho voglia un Pepsi the form "ho voglia di una pepsi" is perfectly correct, just the same meaning
Mi sento di un Pepsi This is not correct, instead and means nothing: you can not remove the verb here (the different meaning allows you to do just everything wit a pepsi....)