Use a hardshell suitcase if possible. A reinforced hard case will give extra protection against breakage.
Place the bottle in a plastic bag. In case the bottle shatters the bag will prevent liquid from leaking all over the suitcase and its contents.
Wrap the bottles in bubble wrap. Cover the entire bottle. Make sure there is a least an inch of bubble wrap around the bottle. This thick layer of wrapping will keep the bottle protected.
Pack the bottles in a suitcase with clothes. Pack half the clothes in the suit case then place the bottles in the middle of the suitcase on top of the clothes.
Pack the other half of the clothes on top of the bottles. The two layers of soft clothes will act as insulation around the bottle.