I'm not really sure there is anything you can do short of having a talk and telling her how you feel, its just not a habit that's easily broken (at least in my own experiences). In the end what options do you really have? You could keep buying her gifts anyway and create bad feelings or limit it to things like birthdays or Christmas. I can sympathize though, someone who can't accept a gift is one of my biggest pet peeves...right up there with not being able to take a compliment, ugh.
The trip thing is harder to get around, by not accepting (weather she knows it or not) it's making it more difficult of you to enjoy something you worked very hard to pay for. Lets face it nobody wants to be out having fun while the person they love is sitting at home...being poor. So what happens? You start living below your means, spending down to her level and before long you're missing out on things you really want to do and bad feelings begin brewing. As much as she may feel she's being responsible, she may not realize she's doing it at the expense of the relationship itself. Its great that you sympathize with her, but as you're girlfriend she needs to start returning the favor and accept that the fellow she loves makes a decent living and doesn't always want to do "extravagant" things alone...she could at least make the effort so you don't always feel like you're enjoying the fruits of you labor alone or having to live below your means just to spend quality time together.
Anyway before I ramble on for a few more paragraphs (sorry it really is a pet peeve of mine) try to find some middle ground, lay off the little gifts and in turn try to get her to understand that you want her along on trips (or whatever) because you love her...its not a money thing its about being together and enjoying her company. If she really doesn't get that then I'm not sure where you go from there.
Hope that made sense...I'm VERY over tired.
Best of luck
