I've had several dwellers make it 5 days or more before running out of Stimpacks. Additionally, when a Dweller levels up they are healed completely, so a SPECIAL 10 dweller w/ Endurance gear can often go a whole day or two before using her first Stimpack. There are events for each of the stats in the wastes, so having everything maxed will give you the best benefit. Once they hit Level 50, switch to your best other gear and give a newbie the high Endurance gear. Dwellers are happier in rooms which correspond to their highest SPECIAL stat. A lack of food, water, or power will bring down their mood. Then put your dweller in your best Endurance gear and send them out. There are several ways of keeping vault dwellers happy: Keep them healthy. If you really want to do well in the wastes, raise all 7 stats to 10 before reaching Level 2. It's also worth noting that at 11 Endurance Dwellers don't take radiation damage in the wastes. So a Dweller who has a 17 in endurance will gain the most HPs each time she levels.

I also gave Commander Fatigues to one of them for 17 strength. The only edit I made with the save editor was lowering the strength of one of them to 1. All dwellers were level 50 with 644 health and max SPECIAL. Whenever a dweller levels up they gain HP based on their Endurance, and this includes the gear they are wearing. Sticking with the Kitchen Knife (3-11) of the previous test, I sent three dwellers on a daily quest that had a level 50 requirement. If you can also equip them with +5 or +7 Endurance gear all the better. However if you want a Wasteland Runner, you should at minimum raise Endurance to 10 before sending them out into the Wastes. Without using a Save Editor of some kind there is no way to see your Dwellers' Max HP stat.

Fallout shelter max dweller level