Chemical water treatment uses tablets or drops — most commonly chlorine dioxide, or sometimes iodine — to disinfect water by killing bacteria, viruses, and (with enough time) protozoa. It's ultralight, cheap, and foolproof as a primary method or backup, but it's slow (often 30 minutes to 4 hours), can affect taste, and doesn't remove sediment.
A UV water purifier uses ultraviolet light to neutralize bacteria, protozoa, and viruses by scrambling their DNA so they can't reproduce. Lightweight and fast with no taste change, it handles viruses that filters miss, but it needs clear water (it doesn't remove sediment), relies on batteries, and treats only small volumes at a time.
A gravity filter uses gravity to pull water from a hung 'dirty' reservoir through a filter element into a 'clean' container, with no pumping or squeezing. It's effortless and great for filtering large volumes for groups or base camp, but it's heavier and slower per liter than a squeeze filter and needs hang points.
A squeeze filter is a lightweight hollow-fiber water filter you screw onto a soft flask or bottle and squeeze, forcing water through the element to remove bacteria, protozoa, and sediment. Compact, fast, and inexpensive, it is the most popular backpacking filter, though it needs regular backflushing and must be protected from freezing.
A wood-burning backpacking stove is a compact stove that burns twigs, sticks, and other found biomass, so you carry no fuel. It offers unlimited fuel where wood is available and a campfire feel, but it's smoky, sooty, weather-dependent, slower, and prohibited during fire bans and in many alpine zones.
An alcohol stove is a tiny, simple burner that burns denatured alcohol (or similar fuel) poured into it, with no moving parts. It's extremely light, cheap, quiet, and reliable, making it popular with ultralight and thru-hikers, but it boils slowly, performs poorly in wind and cold, and is banned during many fire restrictions.
An integrated canister stove is an all-in-one system (such as a Jetboil or MSR WindBurner) that combines a canister burner with a matched, insulated pot featuring a heat exchanger. This makes it extremely fast and fuel-efficient at boiling water and more wind-resistant, ideal for dehydrated meals, but less suited to real cooking.
A closed-cell foam pad is a sleeping pad made of dense foam full of sealed air cells, so it needs no inflation and can't be punctured. It's cheap, lightweight, indestructible, and warm enough for most three-season use, but bulky (it straps outside a pack) and firmer and less comfortable than air pads.
A self-inflating pad contains open-cell foam inside an airtight shell: open the valve and the foam expands, drawing in air to inflate most of the way (a few breaths top it off). This blend gives reliable comfort, good insulation, and durability, but it's heavier and bulkier than a pure air pad.
An air sleeping pad is inflated with air (by mouth, pump sack, or pump) to provide cushioning and, with internal insulation or reflective layers, warmth rated by R-value. Air pads are the most comfortable and packable type and can be very light, but they can be punctured and are noisier and pricier than foam.