Well done. I actually figured out the mechanism early on that ONE was being dropped from seven grid answers and then to look for synonyms when I saw begONE and anyONE and then saw EXIT and WHOEVER. I also from that surmised that WHOPPPER was the probable answer but wanted to prove it.
Unfortunately, since the first two entries had ONE at the end, I got fixated that the other grid entries also had have ONE at the end, which led me to trying PIER ONE and STAGE ONE and OBI ONE, but they led to a dead end.
It took a couple of nudges for me to expand my horizon to look for ONE somewhere in the grid entries - not necessarily at the end, and then everything quickly fell into place along the lines I had expected all along.