Most people only use cartos for flavors they like enough to vape for the life of the carto, then toss the carto and start a new one. Many can get 7-10 days use out of each carto. Avoid juices that drop flavoring sediment in the stuffing to get the best life out of a carto (juices with sediments are usually opaque or cloudy and often but not always dark). And keep them damp. I use thin clear juices, PG w/ 20% or less VG (30% works too, I just think the carto's performance degrades slower with less).
If you are going to carry prefilled spares, put the caps on. And then if you want you should be able to fit 4 Boges in a little plastic 4AA case (cheap on Ebay).
I use manual sealed batteries and just add liquid to the carto as needed to keep it from singeing. I use a plastic or delrin drip tip as a mouthpiece and that is easy to remove to check the stuffing or add liquid.
---- how I fill Boges and other 1ml cartos
The carto has a 1ml capacity. You need to aim towards putting 1ml in. I hold a tissue on the threaded end hole (or put a carto cover's spike in the hole), tilt the carto and drip in 18 drops (waiting longer for the first few to soak in), Then I wait 15 seconds. Then I see how many more it will soak in easily (usually 3-6, occasionally more).
Then I clean it up - clean threaded end, tilt open end down into tissue and puff into threaded end to clear the air channel, then while still pointed down I just touch a soft bit of tissue to the top of the stuffing to sop up excess (to help prevent leaks).
Then I let the carto settle. I use juices with 20% or less VG so 15-20 minutes of laying it on different sides and on end is plenty of time for every bit of stuffing to get damp.
While vaping - any time the vapor seems light, dry, or tastes the tiniest bit off or loses flavor, or if the caro is getting abnormally warm, I add liquid. I also occasionally look at the stuffing (especially before putting a fresh battery on or before going out) and if the top of the stuffing looks white, I add some juice. No settle needed when just keeping the carto damp. And if you do not keep it damp or if you use juice that is too thick (too much VG) you will singe the carto and that adds a bitter taste. I use a simple plastic or delrin drip tip in place of the end cap so it is easy for me to remove that to look at the stuffing or add juice.