Some people use picks and some don't, some can and some can't. I don't use picks on my fingers, but I do use a thumb pick. Very early on, I saw that the great majority of people whose playing I admired used a thumb pick. Not all by any means, and there are notable exceptions like Mississippi John Hurt who played without picks of any kind. So I thought I would try. Originally I used a plastic thumb pick, and two steel finger picks. This proved successful, but for no particular reason I stopped using the finger picks. I think maybe it was because it was easy to clip a thumb pick onto the strings at the peg head or onto the capo, but finger picks just rolled around the place, and got tidied up by my mother and inevitably they were lost. For many years I used a clear plastic thumb pick made by Dobro, but for some reason they became hard to come by so I switched to using Jim Dunlop large size platic thumb picks. I quite like the white ones but really I don't care so long as they fit.
Flat Picks.
I don't use a plectrum or flat pick much these days, and generally I have difficulty finding the darned thing because I can't remember where I had it last, and my wife seems to have taken over my mother's pre-disposition for hiding the things that I want from view. My favoured flat pick when I use one is a heavy gauge large triangular plectrum made by Gibson.
Capos.
For many years, I used a heavy elastic capo made by Bill Russell. It being the only capo that I could find that would hold down 12 strings without muting and stretching them completely out of tune. It had the added advantage of not marking the guitar neck and I could clip my picks onto it. Once again these became difficult to come by. These days I use a Kyser 12 string capo on both the MK53 Gibson and the Avalon L32-12 12 string. Nothing truly works very well on the heavy strung Lakewood D18-12 12 string. I have tried with limited success using a Shubb 12 string capo, and even using both the shubb and the Kyser together. My conclusion is that you can't use a capo on that string configuration.
Slides.
I don't use a slide much. I'm not all that fond of it, but there are a couple of tunes where I noodle about with a slide. I have an old Barnes Mullins Elton Bar that I have experimented with for lap style playing, and also a Shubb-Pearse SP4 Stevens Bar that I like better. For ordinary bottleneck playing I have a couple of Redhouse bottlenecks made by Ian McWee of Diamond Bottlenecks in Stourbridge. These have been made from the necks of wine bottles. (Evidently Italian wine bottles or balsamic vinegar bottles are the best because the Italian glass is more dense that others). Ian also made and engraved a special bottle neck for me that was made from the neck of a vintage champagne bottle that my wife and I shared on our wedding night (actually a half bottle of Dry Momopole 1966, I couldn't afford a full bottle at that time). So now instead of gathering dust in the gas cupboard, it is on display on a shelf in the living room.