I mean, you're really just a slave to your modern luxuries if you need them to achieve a baseline of happiness.
I've spent a lot of time in austere conditions, hiking the Appalachian trail with <20 pounds of gear including food, working in the military with no sleep or shelter, portaging and sleeping in improvised shelters on canoe trips, et cetera. Those are the times that I remember as being the most joyous and peaceful moments in my life. In those moments, when you realize that all that you need to live indefinitely weighs about ten pounds and can fit in a three gallon sack, you are truly free.
I agree that running water, hot water, and the like are convenient and make some things more comfortable, but flushing the toilet or washing my body really don't bring me any joy, and I would be suspicious if they did.
My point is that you shouldn't need anything to produce happiness, because searching for happiness in external things puts you on the treadmill of hedonic adaptation.
Even living in the forest under a pile of debris won't protect you from misery if you don't understand hedonic adaptation. You'll think you'd be SO MUCH happier if you just had a lean-to and a fire. So you build those, and you feel great. BUT, then you'd be SO MUCH happier if you just had an animal skin, so you get one. BUT...
That person is just as pitiful as the person who just can't do without her Keurig or SUV or even bubble baths or whatever, because they're doomed to a life of trying to get happiness from the next new external geegaw.
I think you're taking it a bit far to say that *any* external object should not be a source of happiness. To take your example to an extreme, are you going to say that having enough food or water shouldn't be an external source of happiness? Would you prefer to be alone out in the desert dying of thirst? I don't think most people would be very happy in that situation. You need to satisfy Maslow's lowest level of hierarchy of needs (food, water, shelter, warmth) first. From what I understand of Buddhism, maybe you're talking about striving for supreme non-attachment, or maybe if you're Gandhi you can detach yourself from food for long periods at a time, but at some point most people need *some* external things to be happy.
Punishments like solitary confinement sound horrific. Maybe some stoic and truly self-reliant people could do ok in that situation, but I think I would crack. I need sunlight. I'm an introvert, but I like seeing people every once in a while, and if everyone else on the planet died I'd be devastated and probably start talking to my volleyball Wilson. And I don't want to make it a goal of mine to eschew *all* external things. I like having my husband around, and he is a source of happiness to me - sure, I suppose I could live without him, but I don't want to strive to make him not a source of happiness just because he's external.
Conversely, I do think it's important to cultivate internal sources of happiness, not rely too much on other's people's opinions/seeking others' approval, etc. but I think it's impossible to get rid of *all* external sources of happiness, nor do I think that should be a goal. Loving at least a few others/feeling loved in return, having enough water to drink and food to eat, seeing some sunlight...why shouldn't those be sources of happiness? I would add that in your example, you felt extremely joyful in a beautiful, natural setting. I love hiking and the outdoors because I find the beauty of nature and wildlife to be a source of happiness, and I'm guessing you feel the same. I doubt you would have had those same feelings of happiness if you had been forced to stay in a dark concrete room with your same supplies for the same period of time. Does that mean you should be "suspicious" if being in nature gives you joy?