Well, what do you play already?
Some songs that I play for offering are: "Ooh Child" by Donnie McClukin, "Awewome" by William Murphy, "Stir Up The Gift" by Joe Pace, "In The Sanctuary" by Kurt Carr. Here is how I play "Ooh Child":
Key F LH/RH 4/4 time count in [ ]
*Tip: hold out the chords, hit the bass notes
[1] Bb / F-Bb-D
[an] Bb /
[2]
[3] A / F-A-C
[an] A /
[4]
[1] G / D-F-Bb
[an] G /
[2]
[3] F / C-G, A (slide G to A)
[an] G / B
[4] A / C
[1] Bb / F-Bb-D
[an] Bb /
[3] A / F-A-C
[an] A /
[4]
[1, 2, 3, 4] G / D-F-Bb
(repeat)
[1] Db / Ab-Db-F
[an] Db /
[2]
[3] C / Ab-C-Eb
[an] C /
[4]
[1] Bb / F-Ab-Db
[an] Bb /
[2]
[3] Ab / Eb-Bb, C (slide Bb to C)
[an] Bb / Db
[4] C / Eb
[1] Db / Ab-Db-F
[an] Db /
[2]
[3] C / Ab-C-Eb
[an] C /
[4]
[1, 2, 3, 4] Bb / F-Ab-Db
(repeat)
I just keep switiching back and forth and I use different inversions of those chords for some added flavor. Hope this help you.