GM,
I'm sure you'll be quick to jump all over me as well, but I'll give you my opinion anyway. You lost your receipt, you should deal with it. Period. Why do I have this attitude, you ask? Because I was a department store manager for 4 years. And yes, retail does suck a big fat one.

Why does it suck a big fat one? Because for every person like you who is honest and just trying to make a return with no receipt, there are about 50 who are trying to rip the store off. Not having worked in retail you might not believe that, but I'm telling you the truth. I have no reason to make things up about it.
Put yourself in the store manager's shoes. First off, your whole day (and I mean, the WHOLE DAY) is spent listening to people ##### about this and gripe about that. Have you or anyone you know ever asked to speak to the store manager to tell them how great their store is, or how helpful you found their cashiers, or how impressed you are that every single light bulb in the store is on and that there are no leaks coming from the ceiling? I'd put my money on "No". Nobody ever does those things. The only thing the store manager gets to do all day is listen to people complain. Secondly, it's the holidays. Just consider the fact that not only has this person has had to listen to complaints all day, but they have been working open to close every day for about a month (I know I had to when I was a department store manager). Then think about the sheer volume of people that the manager is having to deal with during the holiday season. You were in the store for an hour shopping. He/she has been in the store 12-13 hours a day for a month listening to people complain. Compare the two.
Now, also consider the fact, as I mentioned before, that a very high percentage of the people the manager deals with on a daily basis are trying to rip them off. You have absolutely no frame of reference of what it is like. My favorite's from my retail days (and this happened much more than once, believe it or not) are the people that bring back shoes. No receipt, they looked like they had been worn for about 3-5 years, and this person tells me that their shoes wore out. They want another pair.

People do this sort of stuff ALL THE TIME!
That's what a store manager deals with all day.
That's why store policies are created. There was a store policy in place, and you tried to go against it. The store manager called you on it, and I commend him/her. Bottom line is, if you had your receipt, it would have been fine. You lost it, which is your fault, not theirs. They followed the policy that they had in place in just such an event. Case closed. You should move on.
As I said before, I'm sure you will lash out at me (just like all the posters above who didn't agree with you), and that's fine. But I think you should look at things from other people's perspectives before you throw a hissy fit and lose your cool. I lasted as a department store manager for 4 years before people like you drove me out of it. At my first store I was manager of, mine was the only store in the whole company that got a perfect customer service store from the company's secret shoppers. And yet, as good as the customer service was, I never had one single customer come up to me and tell me how much they liked my store or the people in it. All I ever heard were the complaints. People think that everything is always about them. If they're not satisfied, they DEMAND to see the manager. And there the poor manager is, having to have someone yell at them for the 187th time that day. Well personally, I'm glad that the manager didn't back down and followed the company policy. That's all that you can really ask of a store manager (unless you're one of these selfish customer types who thinks that everything is about them, and company policies shouldn't apply to them because they are special

)
PS - If you won't use the gift card, send it to me. I'll put it to good use.