We can be a bit snooty about frozen produce over fresh, but actually the process of freezing, say, fish straight away can actually lock in more nutrients. It will also save you quite a bit of cash.
The same logic applies to vegetables and some fruit. This is particularly the case if you won't be able to get through a whole packet of the fresh equivalent before it goes off.
Comparison: The fresh Leap Wild Sockeye Salmon Side costs £15 for 450g (that's £33 per kg) while the frozen Young's Wild Pink Salmon Fillets cost £4 for a 360g four-pack (that's £11 per kg).