Is it wrong to buy expensive food when people are starving?

No, it's not. Those people in mansions with expensive food and stuff (probably) worked hard to make that money. I personally think donating some of it to the poor is a great idea, but it's their choice.

If it is wrong, it's wrong because of a choice that you're refusing to make (donating money) rather than a choice that you're actually making. You're not directly hurting the poor by stealing what little they have; you're indirectly hurting them by refusing them help. Either way, you are still responsible for their pain. If you have the ability to help someone and you turn it down, then you're the bad guy. I mean, maybe it's just me, but it wouldn't rest well on my conscience See More to live in extravagance at the expense of someone else.

Yes, no doubt about it.
Humans are selfish though, and don't want to believe they're anything other then perfect. Humans make excuses for their behaviors.