No magic here you pretty much need a better antenna. A laptop trades portability for good antenna design.

The first thing to try is a cheap USB wireless card you can put on the end of a 15ft USB extension cable. This give you more flexibility in placement. This option only works if your PC will also work at the location. For example you can place the usb adapter in a window and not have to sit their.

If your signal is too low for this you really are going to need a antenna. First step is to get a USB adapter that has replacable antenna. Hawkins and ALFA both make good devices that have small external antenna included. If this still is not good enough then you go to connecting direction antenna to these cards. Hawkins again has consumer friendly models, problem is that when you need to go any distance you are carrying around a antenna that is larger than your laptop. They are not real expensive or all that heavy but not what would be considered portable really.

Stay away from the so called signal amplifiers, they tend to amplify the noise just as good as they do the signal you want.