As soon as you get home sort through your mushrooms. Double check the identity of each and discard any you’re not 100% sure of. It’s worth getting a second mushroom identification book for this double checking as it may make slightly different observations which could help. It will also have another set of pictures to check against.
Clean your mushrooms and trim them to remove any damaged parts before putting them in the fridge. Paper bags are good for storing mushrooms or wrap them in kitchen paper put in a loosely sealed containers. Kept in the fridge like this most species will last several days, some even longer. A few species don’t keep well however well you store them (particularly the Inkcaps).
If you brought back any specimens to closer inspection now is a good time to setup any spore prints you need to take. Its also a good idea to update your mushroom diary now. Keeping a diary of when and where you’ve searched and what you found will prove invaluable for deciding where to go on future forays. If you know that at this time last year a particular field had parasol mushrooms in it, it’ll be worth a visit again. If you don’t keep a diary you’re unlikely to remember which or in which week you found them last time. Modern technology can help here. A handheld GPS will allow you to make a way-point when you find a mushroom and annotate it. You’ll then know exactly what you found where and you’ll be able to navigate back to that point in the future.