I still have and use my Action Replay Mk4 for entering Pokes and backing up single load games to disc. I also use the Fast Loader on it for disc based games so its pretty quick.
I have the Vic 1541 single sided drive, nicknamed the breeze block given its size, have to flip the disc for the reverse side. I also have a standard C2N and a Mills deck which has the lights on it so you can fine tune the Azimuth Alignment for a game if you are having issues loading.
Oh yeah, I had one of those tape decks with the lights and a knob in the hole already so you didn't have to get a screwdriver in there, randomly just died one day though :-( I remember on the original C64 (I don't think it worked on the C64c) there was a poke to hear the loading screech like a Spectrum so you could try to adjust it by ear too!
I also remember cutting a groove out of the side of supposedly one sided floppies to magically make they duel sided too!
My original C64 (Breadbin) still works and I have a 64c also. The breadbin board is in the c case now though as the keyboard wasn't working properly on it and the C64c died a few month back after we had a power cut there must have been a surge.
The original machine SID chip is better than the one in the c as on Myth for example. After title screen has loaded it says Welcome to Myth, on the c it says it but it is barely audible, you can put a resistor between pin 1 and 14 but that can mess up the audio levels in general on some variations.
Yeah, you notched the disk on the opposite side with a hole punch or with a pair of scissors to use the reverse side of the disks, to write protect again just put some tape over the edges.