The obvious question I have is whether the person who asked you knows you will be playing classical and not "cocktail" music, and whether they want 100% classical, no classical, a mix, etc.
If all classical, some movements of Bach suites are good, slow movements, and even selected fast movements of Clementi, Mozart, Haydn. Chopin Op 25#1 is a great thing to play for that type of venue - of you know it.
Some lighter Schubert - Landler, Waltzes, Moments Musicals. Mendelssohn, etc.
Also, all the other suggestions people made are good.
Make sure there is enough contrast.