Buy some
juice.
5 cartomizers should last a month if you keep them damp.
Battery + cartomizer
Cartridges last forever unless you melt them (you can restuff etc) - it's the atomizer that degrades and dies
Battery + atomizer + cartridge
And a note about Ego and T-rex
Cartomizers
Any 510 cartomizers 2-3 ohms should work & the most popular for 510 fat batteries are Boge 510 2 ohm
Ego cartomizers can be different - some Ego clones have a slightly deeper throat and some need a 510 shorty extender to use some (mainly Joye/Joyetech made) Ego cartomizers (I suggest owning a shorty 510 extender from madvapes or Goodprophets)
Cartridges
Slim 9.2mm diameter atomizer uses 510 cartridges
Longer slim 9.2mm diameter 510 Mega atomizer uses 510 mega cartridges (longer inside part)
Ego atomizers are much wider - the width of the metal collar of the battery - they use Ego cartridges
There may also be Ego mega atomizers (longer) that may need Ego mega cartridges (not sure)
tanks
510-T tank atomizers use 510-T
tanks
Ego-T A-size tank atomizers use the smaller Ego-T tanks
Ego-T B size tank atomizers use the smaller or larger Ego-T tanks
I think I have that all correct - I do not use them