A survey of nearly 2,000 people across the UK suggested more than half were trying to make better use of leftover food, the Food Standards Agency (FSA) said.
It noted that some people were "taking more risks with food safety as they try to save money and make their meals go further".
This included ignoring use-by dates, as well as keeping leftovers in the fridge for long periods of time.
The number of cases of food poisoning peaks in the summer as the warmer weather means germs can grow at a quicker rate.
According to research conducted by FSA showed that most of those questioned (97 per cent) believed the cost of their typical shopping basket has gone up significantly in the last three years, with half of these (47 per cent) trying to make better use of leftover food.
However, some people are ignoring 'use by' dates more than they used to, while others are keeping leftovers for longer than the recommended limit of two days in the fridge, the FSA said in a statement ahead of the 'Food Safety Week' beginning today.
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Bob Martin, a food safety expert at the FSA, said: "With most of us seeing our weekly shopping bills increase over the last few years, we are all looking for ways to get the most out of our shopping budget.
"Using leftover food is a good way of making our meals go further. However, unless we're careful, there's a chance we can risk food poisoning by not storing or handling them properly," Martin said.
There are around a million cases of food poisoning every year in the UK. The levels increase during summer months, with around 120,000 extra cases of illness from June to August.
The FSA said a third of people were more likely to use the look and smell of food to see if it was safe to eat rather than the use-by date.
Martin said: "It's tempting to just give your food a sniff to see if you think it's gone 'off', but food bugs like E.Coli and Salmonella don't cause food to smell off, even when they may have grown to dangerous levels. So food could look and smell fine but still be harmful."
The FSA said leftovers should be put in the fridge as soon as possible and then eaten within two days and should be cooked until they are steaming hot.