Sit down with him with pen and paper
Write down all his monthly income
Write down all his monthly bills
Now work out where he can skim the fat
For example
can he change to a cheaper electricity/gas supplier..can he have his meter changed to top up meter so that he is only using what he has already paid for
Can he change his mobile network to a cheaper one or even change his priceplan.. .if he is on a contract, can he change to pay as you go
If he has sky TV/virgin, Netflix etc..can he cancel the subscription and get FreeSat or Freeview (still get plenty of channels with no monthly subscription)
If he has a landline and WiFi can he have it cancelled to save the bill he would pay, he can use his mobile and if he needs internet many places offer free WiFi
If he has a car could he sell it and save the money and walk, cycle, take a bus ...he would save alot
Now that you have skimmed the fat
Calculate how much money monthly he has left...
For food tell him to buy supermarket basic brands ...and show him batch cook freeze websites (where if he cooks a meal using the cheapest foods he can buy, he can portion up what he needs and freeze the rest for other meals...it would save him and make it cheaper to feed his kids when he has them ...
Also if he has any debts can the citizens advice bureau talk to his debtors on his behalf to get any payments reduced to a manageable size for him...also get him to talk to them about his money issues, they may be able to help point him in the right direction.
And if he is short of money there is food pantries too
If he is taking the low paid job because of lack of qualifications could he do an evening class or something to work towards a qualification in something that he would like to work at?...
Will his family and parents help him get on his feet?