bodgejob I am not a lone parent so I hope you don't mind me posting, but my dh works away through the week (not the same in any way as being a single parent I know), so I have experience of dealing with lots of little ones single handed.
I have b/g dts (2) and ds1 (6) dd1 (4) and ds3 (1). I am very organised. Have to be, we use public transport for the school run and bus only runs half hourly. I do the lunches the night before, for all of us if possible, it's one less thing to worry about. I make lots of big meals and freeze the rest to do lunch or dinner on the days I can barely muster the energy to breathe. I also get clothes etc out the night before as suggested. Letters etc from the school get dealt with immediately (dates on calendar, forms signed and handed back same day if possible).
Accept all offers of help and join as many groups as you can. The more time you are out the more hands there should in theory be to help, also the less time your dts will have to wreck the house. Rest during their nap time if you can.
I hope things get easier for you. Do you have a Surestart crèche near to you? I used to be able to drop my dd off for two hours a week to give me a break when pg and it was free. Also some nurseries now offer funded placements from about 2 years and mothers of dts often get higher priority for early placements, it depends where you live.
I usually keep a stash of food on me to keep my dts quiet if I need to speak to the teachers etc. I've had to abandon my buggy now (buses not disabled friendly) but when I used to use it I would keep it stocked with enough stuff for one day (nappies etc).
Sending you lots of positive vibes and hope you don't mind me sticking my nose in.