Here are some options you could use:
Figurative:
* A tapestry of memories: This emphasizes the interwoven nature of memories.
* A treasure trove of memories: This implies the value and abundance of memories.
* A kaleidoscope of memories: This suggests the vibrant and diverse nature of memories.
Formal:
* A collection of memories: This is a straightforward and neutral option.
* A compendium of memories: This implies a complete and organized set of memories.
Informal:
* A bunch of memories: This is a casual and friendly option.
* A stack of memories: This is a more playful and whimsical option.
Ultimately, the best collective noun for memories depends on the context and the desired effect.