We might circulate antifreeze through an optional 12.5"x22.5" rectangular bladder under ice-cube trays in a small freezer http://www.walmart.com/ip/Igloo-3.2-cu.-ft.-2-Door-Refrigerator-and-Freezer/15162473 in series with the U-bladder, in order to cool the cooler without adding ice.
This system has adjustable flow rate temperature control, ie we can vary the pump flow rate manually to vary the cooling. A more advanced system could have an adjustable bladder thermostat to run the pump as needed and measure the dew point of the surrounding air and limit the lower bladder temp to avoid condensation. Air at T (F) (absolute temp 460+T R) and RH% has an approximate (T+460)/(1-ln(RH/100)(T+460)/9621))-460 F dewpoint. For example, 70 F air at 50% RH has a 530/(1-ln(0.5)530/9621))-460 = 50.5 F dewpoint.
If it's humid, air movement helps. The Berkeley online comfort calculator http://www.cbe.berkeley.edu/comforttool/ says 25.4 C (77.7 F) air with a 25 C mean radiant (wall) temp and a 0.15 m/s air speed and a 50% RH and a 1.2 metabolic rate and 0.5 clo clothing is comfortable (PMV = 0.01 on a scale of -3 (very cold) to +3 (very hot)). Increasing the RH to 60% makes the PMV = 0.08 (slightly warm.) Increasing the air speed to 0.17 m/s makes things comfortable again, with PMV = -0.01. So does removing some clothing, with PMV = -0.02 at 0.45 clo. See also http://sustainabilityworkshop.autodesk.com/buildings/human-thermal-comfort and http://wikihelp.autodesk.com/Simulation_CFD/enu/2014/Help/0083-Tutorial83/0334-Tutorial334 and http://www.labeee.ufsc.br/sites/default/files/disciplinas/Thermal%20Booklet.pdf
Losing weight also helps, allometrically-speaking, ie increasing our heat-losing-surface-to-heat-generation-volume ratio. The ASHRAE Handbook of Fundamentals says a W-pound animal generates P = 6.6W^0.75 Btu/h of heat, and a W pound x H inch tall person has A = 0.108W^0.425H^0.725 ft^2 of DuBois surface area, eg P = 289 Btu/h and A = 19.6 ft^2 for a 154 lb 68" tall ASHRAE-standard human, who might be dT = P/(1.5A) = 9.8 F warmer than surrounding still air if naked, with no sweating or shivering or other adaptations. Raising W to 200 lb makes P = 351 Btu/h and A = 21.9 ft^2 and dT = 10.7 F, with H = 68". A proportional height gain to H = 12.7x200^(1/3) = 74.2" raises A to 23.3 ft^2 and lowers dT to 10.0 F.
See also: http://theoatmeal.com/comics/running