My girlfriend just told me that I have to give her a gift every six week to show that I care or she's going to break up with me?

I suggest that you don't even respond to her and get on with your life without her.  From today live as if she never existed.
If you act upon her wishes you'll live to regret it and the relationship will not last very long anyway. 

Why in the world would you even consider being in a relationship with an abusive bully like this?  Tell you what--when Monday comes and she comes around expecting her present, you say to tell, "Guess what!  I have something special for you.  I'm telling you that as of this very minute, I'm breaking up with you!"  Then, turn around and walk off.  Expect her to throw a royal 2 year old tantrum.

Dump her......................

move on.......................

Get her a box of chocolate. Let her get fat. She’ll beg you to stop giving her gifts. Problem solved. You’re welcome. 

Tell her to get lost.

Strap a pair on and flip her the bird.

She's not your girlfriend, she's a callous user.  Dump her and call it a lucky escape.

Give her the perfect gift of breaking up with this gold digger. If you do this, I want you to send me a gift every 4 weeks too.

She is not in love with you but just whoring for gifts etc.