A good zoom is probably your best bet for more random situations where you could need wide and zoomed in the same setting. In situations I can only take one lens, I use my Nikkor 18-200mm, just very versatile and I've always been pleased with the results. Not sure if there is a Canon counterpart.
For a prime that is slightly wider, I've been super pleased with the Sigma 30mm 1.4. Indoors it's wonderful, especially in places where the 50mm is just too much zoom.
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