My girlfriend just called and said that she’s feeling horrible today, and that her cramps and whatnot are much worse than usual. I feel bad for her so I’m soliciting advice to see if there’s anything I can do for her so that when she comes home I can say “Aha! Look what I have for you!” and then put her to bed. Midol? Chocolate? Ice packs? Demerol? I really have no idea and I don’t want to ask anyone who’s handy. Besides going away and hiding in my den what else can I do to ease the pain?
Sex.
ETA: Sorry, that seems flippant, but I was serious. Sex - or masturbating as well - helps with cramps for some women.
Chocolate is usually good.
Also, do what you can to make sure she doesn’t have any chores to do this evening. Even if there’s nothing she has to do, make sure that there’s nothing that she feels like she ought to do–like straighten up or whatever. That way she can just lie on the couch and whine.
And most importantly–don’t do that “male” thing where you offer all sorts of suggestions of how she can ease her discomfort and so forth. She knows all that. Just offer sympathy (and chocolate).
Oh yeah–you can offer her a foot rub. She might well say no, but she’ll appreciate it.
Sweet and salty–chocolate and potato chips is what I usually end up with. If you have a Trader Joe’s nearby they have these delicious chocolate covered peanut butter filled pretzels that do the trick for me.
Back rub–get your thumbs right in over the kidneys and rotate with medium pressure; don’t stop until she collapses. Then get her feet and do the same thing with her insteps. There’s a pressure point there that anesthetizes cramps. Make your movements deliberate and leisurely–don’t be herky jerky or she’ll come unglued on you.
If she doesn’t have a heating pad or hot water bottle, get her one and fill it whenever it cools down.
Be very calm and soothing, see if you can get her to sack out on the couch with her head on your thigh. From this vantage point you can get to her lower back and also rub/scratch her head. Get her to sleep if it’s at all possible.
Aleve. Works better for cramps than anything OTC I’ve found.
Demerol’s great if you have it–but weed works too if you’re inclined that way.
Good luck! 
The only thing missing from SmartAleq’s list is a hot bath.
I will second the suggestion of a hot water bottle / heat pack / Magic Bag suggestion. I have to admit, as much as I love The Boy, I love my Magic Bag even more when I’m achy and crampy and hormonal.
Aside from that, go with the standard sick-GF routine. Wrap her up in a blanket, give her a hot cup of tea, and do the dishes while she’s lying down feeling miserable.
Also, call her up and tell her you’re bringing home the takeout of her choice.
If I’m having a crappy day (for whatever reason, actually), the sheer knowledge that I need not worry about preparing dinner and subsequent clean up almost makes me giddy.
Just spoil her really. Do you have a big comfy sofa near the TV? Arrange lots fluffy pillows and blankets, put her in it, rent something she loves and just get her whatever she likes. My favourites would be something like a huge cup of hot chocholate with whipped cream, or hot milky tea with honey, but get whatever she likes. Be fussy and do the gentleman thing - gently forbid her from doing any household chores or contributing, if they need doing, do them yourself.
Nice. I can manage all of this stuff. I’m off to Walgreens for pills and a heating pad, and then the pizza place for the super garlic pizza. The whole house will be straightened out, and her favorite comforter and her pillows will be on the couch. I won’t even bitch if Rock of Love comes on. Back rubs and foot rubs will happen if wanted and I think that sounds like a good list so far.
You, sir, are a keeper. I hope she knows that. 
Scarlett, who got a keeper herself
Hey, I’m only following the good advice I came to get in the first place. I can’t be taking credit for anything!
We’ll clone you first.
I hope it all makes her feel much better.
Dude, first you ASKED for advice and now you’re going to FOLLOW it?? I call BS here–you’re definitely a keeper! 
Pot, red wine, and chocolate seem to be fairly effective, and orgasm can ease cramps. From what my field notes say.
Not only is he following the advice, he’s probably not even going to take credit for it when he gets home with his pampering supplies. I’d bet you he admits he’s wrong in arguments and stops to ask for directions when lost, too.
Note to self: update will to request burial with ice skates, because hell hath frozen over.
CLONE THIS MAN! For the benefit of all womankind.
I know this is probably too late, but chocolate covered pretzels when I’m PMSing are boss.
And admit it, you watch Rock of Love for the boobies.
Wait, wait… you are male? Damn.
Got a sister?
Careful budgeting of your money is important. If you are running into problems, then see what you can cut out. Often expenses which are thought to be necessaries aren’t really and you can get by with less than what you first thought.
OH, you mean THAT time of the month. I was thinking you were talking about when the rent was due.
In addition to the great advice from others, I’ve found flowers, cooking dinner; served in bed and then washing dishes while she watches TV bring bonus points, even if they don’t help her feel any better.
Pampering your love when she hurts or is sick is worth, something like 1,000 times more than expensive Christmas presents.
Success! I stopped and got the heating pad and a last minute phone call changed things from pizza to pad thai and red wine, which is always cool with me. The offers for foot and back rubs were not taken, but she did get nice fluffy blankets and total control of the remote. As a matter of fact the heating pad was such a hit that I think it might become part of her day to day outfits. 
I can’t believe we never had one of these before.
Thanks again for everyone’s input, you all really helped me save the day.