We need more specifics. Geography and climate, weight expectations (UL, SUL, fantatic UL), personal physiology (sleep hot/cold, etc). Do you want to start from scratch or build around the gear you have?
Here's my generic list of UL gear gleaned from forums here:
Pack: as small and light as will fit the job. Simple is good. Heavy suspension features aren't needed with light loads.
Trekking poles: integrate with shelter and lighter footgear.
Shelter: tarp, poncho tarp, cape shelter, or hammock system. Add bivy bag for more exposed shelter types. Add bug protection to personal comfort or disease protection.
Rain gear: Poncho or cape. Add chaps or pants to suit.
Kitchen: small compact heat sources--- alcohol, Esbit or UL canister models. Titanium mug/pot, spork. Foil windscreens.
Clothing: integrated layered system. Polyester or wool blend base layer, breathable light midlayers, down, polyfill, or fleece insulation layer, windproof and breathable out layer. Accessories: gaiters, gloves, hats, bandana.
Footgear: trail running shoes. Thin wicking socks.
Sleeping gear: UL pad (closed cell, hybrid foam/inflatable or insulated air mattress), as small as you can tolerate. Ground cloth: thin waterproof membrane. Bedding: down or polyfill quilt or mummy bag. Add bivy bag to suit shelter type.
Hydration: light bladders. Filter and/or chemical purification.
Knife: small, light, simple
Lighting: small LED sources
First aid: light and compact, good blister care.
Navigation: compass/GPS and maps to suit experience and terrain.
Fire starting: small butane lighter, waterproof matches or case, spark generator, tinder.
Signal devices: whistle and mirror
Extra food: hard candy, energy bar
Personal hygene: plastic trowel or other light digging tool, TP, hand sanitizer. Biodegradable soap, small toothbrush, floss, comb, small pack towel.
Food: caloric intake suitable to trip. Dehydrated meals, hard cheeses, dried sausage, beef jerky, rice, oatmeal, nuts, dried fruit, energy bars, candy, dried soups, coffee, tea, hot cocoa mix, electrolyte drink mixes, pilot crackers, pita bread, bagles.
Add ons: camera, journal, radio/music, book
Concepts and tips:
The items that will lighten your load the fastest are the Big 3: pack, sleeping gear, and shelter. I would add clothing for the Big 4.
Less is more
Keep it simple
Take only what you will use-- cut accessories to the minimum
Weigh and analyze everything
Don't fight or fear nature: understand it instead.
Decant liquids into small containers
Create an integrated system
Seek multiple use items