Calculate your maximum budget for christmas presnts without adding to your overdraft (if you have got one.)
Divide this budget between the number of people you absolutely have to buy presents for.
Really think and search for a present within the per person budget. Do not exceed it.
If you run out of money, look at what you could reasonably pass on as a present that you have already at home, (maybe an unwanted book for example). Or make something to give away.
Most important do not feel guilty for what you cannot afford to give. Instead give of your time, write a letter, make a phone call, to the person to make them feel they are not forgotten.