Hitting some road blocks

Thomas had a pretty good field trip to the park with his class yesterday.  He brought a joke can of nuts that has a snake pop out and showed the teachers.  He was excited to do this.  This attracted a lot of children and he had another panic attack screaming he wanted to go home and crying.  Eventually we got him to calm down, but it affected his mood the rest of the time.  He did say bye and wave to his teacher when we left.    I have tried very hard to engage Thomas in other activities and games with children but it is always met with resistance.   We are hitting a lot of road blocks with him and are feeling very frustrated.