Half my thyroid was removed, with no ill effects after 30 years or so.
In general redundant body parts would require energy, and that would be evolutionarily disadvantageous, especially in times of food shortages. So we’d expect that unless there was an advantage it would not be sustainable.
Consider computer systems. (I just wrote a column comparing the fault tolerance of the body to fault tolerance of computers.) Triple modular redundancy takes up space and energy, and so doesn’t get used except in cases where reliability is really vital. Multiple core or processor systems are much more popular since they will still work if there is a failure but increase processing power even if everything is okay.
It’s called Bilateral symmetry and it applies to nearly all the human body (and also most mammals).
Look at the head, for example. Two eyes, 2 ears, 2 nostrils, 2 sinuses, 2 sets of teeth (sets of canines, incisors, bicuspids, etc. on each side), even 2 semi-independent halves of the brain (and you can live with only one)*. Many of the glands, like thyroids, lymph nodes are doubled. And the kidneys, as the OP mentioned. Even the critical heart has 2 halves, and people can live with only part of it working correctly. Most of the external body is so: 2 arms, 2 legs, 2 sets of fingers and toes.
Only when we get to the energy-production part (digestion) does the body limit itself to one: 1 tongue, throat, liver, stomach, intestine, colon, anus. (But note that this is way over-sized; people can lose way more than half the liver and still function; the stomach can be greatly reduced (gastric bypass/band), large sections of the intestines can be removed, etc.
In the most critical system (evolutionarily) of reproduction, we have fully redundant spares: 2 testes or ovaries, and still fully functional with one set gone.
So, in fact, it is more common for the human body to have ‘pairs’ of organs than not. So the OP’s answer is ‘most of them’.
Evolution has started to take advantage of these ‘spare’ parts by doing some specialization in them. For example, the 2 halves of the brain tend to specialize in separate functions. Especially in right-handed vs. left-handed people. And that handed-ness itself is a bit of specialization from physically paired hands/arms.