This term will mean different things to different people. When I think of gunk holing it brings to mind lazy sailing and exploring in protected bays and estuaries and rivers. For this type of sailing your cruising boat can be as small as you wish; a considerable amount of this type of activity is undertaken in open boats. When it is time to anchor at night, a boom cover often serves as a shelter. Portable gas or primus stove and a bucket may be all of the 'appliances' carried on this cruising boat.
The right boat and an inquisitive mind are two important qualifications when considering gunk holing. Shallow draft is a major benefit when considering this type of cruising. Once the water gets really thin you will no longer be able to rely on your depth sounder so you will literally have to feel you way in many of these areas. Detailed charts of the area you are exploring are essential, if none are available then it may be fun to make your own thus enhancing the enjoyment of the current trip plus adding to the enjoyment of future visitors to the area.
Nature watching is one of the many attractions of gunk holes. You may also find unusual man made oddities; follies, abandoned fishing and other commercial operations, historical relics and occasionally a human eccentric. On reflection I can claim to have encountered all of the above and they all bring back pleasant memories.