Another vote for mini hot dogs. The frozen Hebrew national ones are also good.
And take a look at this link to Bao Bee's catering menu. They are a small company so might be amenable to assemble mini's for you.
https://baobei.menu/menu
For a spurge, O'Donnell's crab dip served with crackers. You would want a chafing dish. Delish, went in 10 minutes when I brought it to a party.
Founding Farmers does catered sliders and deviled eggs.
https://www.foundingfarmerscatering.com/_files/ugd/f148bf_df6d8dbf8b8c4d23afa8e01dee597172.pdf. This would make the whole thing easy for you.
Or, what I've seen is Shake Shake burgers in envelopes at parties. This goes over very big and they were fine at room temp.