quiero lo que pueda darme
what does this mean in english
Using subjunctive in a case like this where it would make perfect sense in the regular form actually adds an "non-definitive" sense to it. Words such as "wherever" "whenever" "whatever", etc can be expressed nicely with subjunctive. In this case rather than simply "I want what he/she/you(formal) can give me", it says "I want whatever he/she/you(formal) can give me/might be able to give me."
I want what you ( formal:usted) can give me, or I want what he/she can give me.