For me it's:
1. Gasit refillable gas bottles and external fill point. These have now paid for themselves but far more importantly I haven't wrestled with a Calor bottle in just over 2 years!
2. 300W solar panel, solar controller and battery monitor so I don't need an EHU even in winter (I'm not a big power user).
3. An extra leisure battery.
4. An internet radio so that I can listen to pretty much anything, pretty much anywhere.
5. LED lights in all the original light fittings.
6. Purpose made storage for pots, pans, cutlery and crockery so that everything is to hand and nothing rattles!
7. A Hozelock patio cassette hose and every variation of end fitting I could find.
8. A homemade fitting with an on/off valve that connects the hose end to the water tank inlet.
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I've just realised that you're thinking I'm a really sad old moho-er so I'll stop here.
Colin ???