The COVID-19 pandemic has affected the lifestyles and training of elite athletes around the world. The detrimental effects of lockdown periods may vary among individuals, as well as among sports and sexes. This study investigated the changes in dietary habits, and the predictors of perceived stress during lockdown and a “bubble” training camp. This cross-sectional, online survey involved 76 elite and world-class athletes from six able-bodied sports and nine parasports, all of whom were involved in a 30-day “bubble” training camp. Questions were asked on socio-demographics, training routines and wellbeing, perceived stress, and dietary habits, pertaining to “normal” training (prelockdown), lockdown training, and “bubble” camp training periods. Changes in perceived stress were trivial to small during lockdown compared to “normal” training, and trivial to moderate during a “bubble” camp, compared to lockdown. Para-athletes, males, older athletes, less experienced athletes, married individuals, and specific ethnicities appeared to be more detrimentally affected (increased perceived stress) by lockdown. These negative experiences, however, were largely reversed during “bubble” camps. During lockdown, more athletes reported increased evening snack consumption (+8%), later meal-times (+6%), decreased fluid intake (−6%), and no breakfast (+7%). These changes were reversed during “bubble” camps (12–18% improvements). Sport classification accounted for 16% of the increased perceived stress (p = 0.001) during lockdown. Overall, socio-demographic factors, improvements in training routines, well-being, and dietary habits explained 28% of the decreased perceived stress during a “bubble” camp. In conclusion, better dietary habits, training routines and well-being have implications for reduced perceived stress. During lockdown, “bubble” camps may be beneficial, but this observation may be a case-by-case consideration, and short split “bubble” periods are recommended.