Protein powder: yes, with conditions

For

• 1 serving (30 g) = 24 g of protein and 120 kcal with just 300 mL of water; no gas, no cooking, no cans to open.
• 1 kg equals ~33 cans of tuna in protein (5 kg of weight). For evacuating by car, there's no comparison.
• It fills the gap in weeks 3 to 5, when the cans run out and the diet turns into rice, pasta and oats.
• Real shelf life: studies of whey protein show more than 12 months even in heat and humidity, and up to 19 months at 21 °C (70 °F) and 35% humidity.

Against

• Per calorie it costs 10 to 20 times more than rice. It can't be the base.
• It has no fat or fiber. Without enough calories, the body burns it for energy and the point is lost.
• Heat punishes it: at 35 °C (95 °F) and 45–65% humidity, its shelf life drops to ~9 months. An apartment without air conditioning in midsummer is in that range.
• Opened, it lasts less: plan to use it within 6–12 months of opening.
• The water it uses counts against your drinking water.

Doing it right

• Whey isolate or a whey/casein blend; if someone at home handles lactose poorly, pea protein or a plant blend.
• Sealed tubs, not opened bags. In the coolest interior closet; never next to the water heater or on the balcony.
• Rotate yearly: buy it to use in normal life and replace it, so it's never stored more than 12 months.
• Whole powdered milk is the most complete and cheapest "protein powder" (fat, protein and carbs); that's why it's in all three levels.