Can I select a spell that doesn't use a slot as a contingent spell?

Question

From contingency:

You cast that spell, called the contingent spell, as part of casting contingency, expending spell slots for both [emphasis mine]

Does this mean that the spell chosen must be one from the Spellcasting or Pact Magic feature that uses a spell slot?

(i.e. not from a racial trait, magic item, feat, or a cantrip)

Answer 1

Probably Not, but equally Possibly Yes

This is very similar in language to Ring of Spell Storing to which Jeremy Crawford has provided guidance.

Contingency requires:

Choose a spell of 5th level or lower that you can cast, that has a casting time of 1 action, and that can target you...You cast that spell--called the contingent spell--as part of casting contingency, expending spell slots for both...

Ring of Spell Storing requires:

Any creature can cast a spell of 1st through 5th level into the ring by touching the ring as the spell is cast...The level of the slot used to cast the spell determines how much space it uses.

Both the spell and the item require a spell to be cast into the ring, although while Contingency seemingly includes Cantrips (as less than 5th level), it also stipulates that Spell Slots are expended (which a Cantrip doesn't.)

Jeremy Crawford was asked if someone could cast a Wand into a Ring of Spell of Storing and he responded with:

Casting a spell into a ring of spell storing does require a spell slot.

and

It requires a spell slot. A wand doesn't expend a spell slot.

The implication with the Ring is that the means do matter and the spell being cast into it must utilize a Spell Slot.

But is this applicable to Contingency?

Basing a ruling from an item and using it on a spell isn't foolproof and may even be foolhardy. The mechanics are similar, but not identical. The intent for the Ring is clear, but that Ring also has to track spell level for the purposes of the Ring itself and how much can be stored in it. It's unclear if Jeremy was referencing that mechanic or the casting into mechanic.

You and Your Table

Given the ambiguity, it's going to likely be up to the Table. Contingency is generally a multi-day spell and burning a resource one Day one that will have been replenished by the likely time the spell Triggers isn't that big of a deal. Burning a resource (1/day) for a racial spellcasting trait seems an equal trade-off, suggesting that allowing this is not a big deal.

Answer 2

Yes, but only if you can cast it yourself

Contingency States:

Choose a spell of 5th level or lower that you can cast, that has a casting time of 1 action, and that can target you. You cast that spell--called the contingent spell--as part of casting contingency, expending spell slots for both, but the contingent spell doesn't come into effect.

Under Spells, Cantrips are considered level 0 spells. (Source)

A cantrip’s spell level is 0.

Thus, a cantrip can be used. The requirement to expend a spell slot is merely "double checking" that you are indeed casting both spells. Read again...

You cast that spell... as part of casting contingency

You cast both spells at the same time, using material components for both, consuming any required by the contingent spell, using verbal components for both, and somatic components for both. However, only 1 action is used in total.

As you've correctly pointed out, it can't be part of an item or feat or racial feature unless those items specifically add spells to your spell casting ability. If any item, feature, or trait allows you to cast the spell yourself and is worded that way, then it can also be used, provided it's spell level is 5 or lower.