The wafers will have lost any nutritional value and the expiry date really applies to an unopend container. Once food is opened then it will start deteriorating even if stored correctly.
Cucumber will float so try weighing it down, just pushing the handle of a spoon or fork through it is often used or a plant weight. You can buy things like a Screwcumber
but most people adapt something to do the job of weighing it down.
There is a list of veg you could feed Here
P.S Why don't you introduce yourself in the new members section