As a Highland piper who also plays uilleann pipes and whistles, I've played at hundreds of funerals over the last 40 years.
If I'm playing uilleann pipes I'll just play a selection of Irish airs. Being that I'm in the USA means that at many "Irish" funerals my audience will usually mostly consist of Americans of Irish ancestry, with a smattering of Irish-raised people.
The tunes I choose reflects this hybrid audience. The songs most Americans of Irish ancestry think of as "Irish" were actually written in New York in the early 20th century, or they come from the 1960s "folk music revival". I'll play some of those tunes interspersed with
sean nos airs and perhaps some Carolan.
Much too depends on the venue and the denomination.
There are denominations that require that only Sacred music be played within the church. There are denominations that only allow tunes which occur in that denomination's Hymnal. Hence my collection of Hymnals.
For the Catholic Mass, the Mass itself contains Service Music, though there are points when non-Service Music might be played. Still this should be Sacred music. I generally play pre-service music which need not be Sacred.
In any case at funerals some, most, or all of the music I play might be Hymns.
Bretton wrote:
I've found some others, but they either go too low or too high, or are in keys with bunches of flats.
About the keys and ranges you happen to find tunes in, you'll need to transpose the tunes to fit the whistle.
Pretty much any tune will fit into the standard range of the whistle, if you put the tune into the right key.
What key you actually produce a tune in depends also on what whistle you happen to use. A guitarist should have a capo so your man should be able to accompany you regardless.
To take one tune as an example, BUNESSAN, most commonly used for the
Hymn Be Thou My Vision, yes it almost always occurs in Hymnals in three flats, in the key of E flat Major.
On a D whistle it fits best played in the key of G Major.
To produce the tune in the written key of E flat Major you merely need to play it on a B flat whistle. (That's by far the most use my B flat whistle gets! I have to play that tune at every church gig, seems like, and they always sing it in E flat Major.)
So it doesn't matter at all what key you hear a tune in, or find the sheet music to a tune in. You transpose it to fit under the fingers, and then if it's required in a specific key you use the required whistle.