Sea to Summit "eVent Compression Drysack" - Large - $59.99

The original and still the best. The first compression drybag that uses fabric to purge excess air rather than a valve. eVent permeable fabric is used on the base which allows air to escape but doesn't let water come in. The body is made of a tough 70 denier polyurethane-coated fabric. Base diameter 23cm, height 50cm (20L uncompressed, down to 6.5L compressed).