You said in the OP that you dropped out because of the course content and other reasons. Are you thinking of going back to University this Autumn on a new course?
If you did voluntary work, you do not need to do a full week. If you are claiming Job Seeker's Allowance, there is a limit to how much you can do.
If it was me choosing from that link, I would chose two opportuniities to do one day a week at each. Then if you much prefer one to the other, you can drop one, and concentrate on the other. Also try to consider whether you would like a job at the place in question, one might come up while you are there.
Doing two days, still gives you plenty of time to attend interviews, fill in application forms, etc etc, and still a three day weekend.
User suggested an Agency. A good idea,
but, and with a very big
but, from my experience,. While working for an Agency you are representing both the place you work for and the Agency. A good Agency will guard its reputation very highly. Ask around in your area, who has worked for an Agency, and would they recommend them.
BTW, I have just read Chuffy's post that he added while I was writing this. Working for an Agency will mean you to have to "hit the deck running", fit in without any glitches whatsoever, and know what you are doing.