So I'm working on the particulars of an outdoor puzzle and maybe a few more sets of eyes might help firm things up. 

The terrain the party will be passing though is a rocky mountainous area with a wide rushing stream nearby. In this area the party will encounter a quartet of statues representing four primordial powers; Imix (Fire), Yan-C-Bin (Wind), Ogremoch (Earth), and Cryonax (Ice) or Olhydra (Water). Each statue will be seated in the center of a quadrant venn diagram of four magical circles. Where each circle to the left and right overlap, a pedestal with an offering bowl stands. In the center of the overlapping four circles, an empty chalice sits.

The plan is to have the players learn the history of these elemental primordials, and then work out offerings for the overlaps (mud for water and earth, glass for fire and earth, fine dust for earth and wind, etc.). As the offerings are made, the chalice fills. Once full of elemental energy, a prized potion will be created. 

However, I'm having some trouble working out good offerings for certain combinations like wind and fire, or what to do if my circles include ice instead of water (fire and ice is water, but what is earth and ice or wind and ice?). But water is kind of bleh too with fire and water being steam, but what is water and wind?

Anyway, some ideas would be nice. 

I don't know if this'll help much since not all of it is entirely intuitive, but in some material, there are para-elemental planes at the borders of the main four elemental ones. Magma (fire/earth), ooze/mud (earth/water), and ice (water/air - a conceptual stretch, but it answers the question) seem useable, though smoke (air/fire) doesn't make a lot of sense to go in a bowl... ash, maybe?

Water and wind sounds like a hurricane. So maybe lightning? Though I actually agree with ice — the air makes the water cold, I guess. 

Agree Wind and fire could be ash.

And I’d go with Fire and Water being steam. 

Also I’d go water over ice. Water feels like the more primal force. And then it allows for ice in the combo. 

Seems good. I just liked the look and feel of Cryonax  over Olhydra. 

Ash is a solid suggestion. And rightly, any other weird stuff the players come up with and can justify will probably work. I am just looking for some good sensible options that I can steer them towards if they are stymied. 

I had a puzzle in my blog where the players have to find and capture images from around a magic garden of items that contain a combination of two elements. (In my puzzle, they're given magic stones which can capture a feeling, so that I could use non-material items. I also didn't use ice. Still, perhaps this will be helpful.)

Air & earth

• Leaves blowing about their faces
• The scent of flowers wafting through the air
• A butterfly leaving its cocoon
• Dandelions
• The howl of wind moving between cliffs
• Metal wind chimes

Air & fire

• Lightning
• Starlight
• Fireflies
• Incense
• The phoenix (perhaps a picture of)

Air & water

• Raindrops
• Dew
• Spray off fountain
• Sailboats (I suggest as decoration along rim of fountain)
• Dragonflies

Earth & fire

• Stones warmed in sun
• Coal
• Fire ants
• Gems or glass reflecting sunlight (I suggest as decoration of fountain)
• Poisonous snake, brightly colored

Earth & water

• Moss
• Grapes
• Pottery
• Cactus
• Smooth river stones
• Blood or decomposing animal

Fire & water

• Rainbow
• Acid
• Geyser or hot spring
• Cooked fish
• Fire lilies

as long as they have presdigitation, they can make any matierial they want, so get wyrd

Quote from Capatin_Crunch >>

as long as they have presdigitation, they can make any matierial they want, so get wyrd

 As a note, that's not how the cantrip works at all.

• You create an instantaneous, harmless sensory effect, such as a shower of sparks, a puff of wind, faint musical notes, or an odd odor.
• You instantaneously light or snuff out a candle, a torch, or a small campfire.
• You instantaneously clean or soil an object no larger than 1 cubic foot.
• You chill, warm, or flavor up to 1 cubic foot of nonliving material for 1 hour.
• You make a color, a small mark, or a symbol appear on an object or a surface for 1 hour.
• You create a nonmagical trinket or an illusory image that can fit in your hand and that lasts until the end of your next turn.

I assume you mean the last option, but as an "offering," that material wouldn't last long enough to complete the "ritual."

Anyway, players took a bit, but had an interesting time working out fun materials to use to complete the puzzle. The various lists posted above were helpful to use as some guidelines.