Good points made by all, especially Optimize and hannabee. Users know who to ask for favors and helpers usually feel guilty to say no. I remember watching Oprah many years ago and she said at the time, she had a big problem with saying "no" but had learned its very important. First of all - if someone is asking a question, there's 2 choices, yes or no. You have the right as a person to say no and not even give a reason why. Also women are notorious people pleasers, most of the time because we're are natural nurturers.

Yes your neighbor is taking advantage of your kindness, to ask you to run this favor when you're responsible and have a job interview. You have the right to say no, anytime you want. Favors should be a 2 way street - give and take. What do you benefit from this friendship? Beer and cigaretttes aren't necesseties and she needs to get them herself. Practice saying no with made up scenarios - its a challenge at first to say plain "no" with no sorry or reason. Save your yeses for people who won't take advantage and even then be chosey. Good luck and don't feel guilty.