"It was not a good memorys" - the plural of "memory" is "memories". In any case, the plural does not fit in the context you are using it. If you are talking about something unpleasant that happened, you should say, talking in the present, and thinking back to it, "It's not a good memory".

Numerous means many, a lot. Anywhere you can use those two terms you can use the word numerous instead, but it's a bit more formal.

"The picnic" here means the basket or other container in which the food and utensils for the outdoor meal (also the picnic) are carried.