I've been thinking about getting some things like these:
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One of the downsides is that obviously in many cases you would need more than one board per set, for various alternative modifers and keys and whatnot. But, I like it better than just putting keycaps in ziploc bags, which is pretty much my current method.
It's a no-brainer for me. I just need to get more people to vote or add ones I haven't found. The Originative one doesn't support SA profile keycaps. Mostly just GMK and Cherry.