There could be several scenarios behind this, but a late move to a full flight can mean that they won't have the food tray loaded for you, but the bar should be OK, so I wouldn't worry about that. Moreover it's possible someone will decline a meal, finally if CE then the cabin should have small packs of shortbread and nuts available. If you wanted to do the right thing, by all means look out for the lounge supervisor and explain the situation, they may be able to wrap you some food in cling film for you for example.