No dvd at home, only a 4GB usb stick but in need to install Fedora on a laptop..

and then you realize that the iso image is slightly more than 4gb (ie. Fedora-18-x86_64-DVD.iso is about 4.3GB).
Here it comes isomaster. Just install it via yum:

yum install isomaster

Launch it and select the path where your iso image is saved. Isomaster will open the iso and let you navigate inside the directories and the files contained by the image. Now you can delete unnecessary files until you have the desired size. For example, if you plan to use Gnome as desktop environment, you may safely delete all KDE-related packages (navigate to the “Packages/k” directory, select all the packages starting with kde* and then hit DEL): you will end up with a 3.7GB iso that now you can burn into the 4GB usb stick via unetbootin.