I believe 1995. Here is from a 1995 Kingdom Ministry. The 1994 KM's were business as usual.
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FurtherStepstoBeTaken: We look to Jehovah for his blessing as we move forward progressively. We are happy to see that he has given his people the needed spirit of wisdom and understanding. We must agree that through the faithful slave class, Jesus Christ has directed matters efficiently for the outworking of Jehovah’s purpose in a marvelous way. (Matt. 24:45-47; Col. 1:9, 10) An announcement in the December
OurKingdomMinistry stated: “Beginning with the 1995 district conventions and the September 1995 circuit assemblies and special assembly days, there will be no food served. Each one is to bring his own food and drink.” Circuit assemblies and special assembly days will continue with their present simplified food service arrangements through August 1995. There has been a positive response to this announcement. You may be interested in knowing how this change will be of benefit. Perhaps the following review of adjustments that have been made in recent years will prove to be a good reminder of the benefits we have already received by simplifying the work at conventions.