Functions that are most commonly used should be in an easily-accessible module (such as src/cryptobible/__init__.py). Functions which are already part of the dependencies of this module should not be included here. Same goes for functions that are not useful in a script by themselves and can be achieved using online tools (like xor key length or frequency analysis). Some functions include:
bytes_to_int() (This can already easily be achieved in Python using int.from_bytes(...))
int_to_bytes()
pad()
unpad()
base_convert() : Should work with lists and strings
str_to_dict: combination of json.loads() and sage_eval() for lists of numbers
dict_to_str()
xor(): Similar to pwn.xor()
Please do recommend more if they come to mind